Update to sagemath 8.6.

Also:
- Install an SVG icon instead of a fixed size (128x128) icon.
- Require hicolor-icon-theme since we install an icon.
- Drop obsolete Obsolete.

sagemath-escape.patch

@@ -1,6 +1,5 @@
-diff -up src/sage/combinat/crystals/alcove_path.py.orig src/sage/combinat/crystals/alcove_path.py
---- src/sage/combinat/crystals/alcove_path.py.orig	2018-12-22 16:37:07.000000000 -0700
-+++ src/sage/combinat/crystals/alcove_path.py	2019-01-04 11:16:55.320833974 -0700
+--- src/sage/combinat/crystals/alcove_path.py.orig	2019-01-14 17:16:01.000000000 -0700
++++ src/sage/combinat/crystals/alcove_path.py	2019-02-07 15:43:21.188614487 -0700
 @@ -383,7 +383,7 @@ class CrystalOfAlcovePaths(UniqueReprese
  
          One can compute all vertices of the crystal by finding all the
@@ -10,9 +9,39 @@ diff -up src/sage/combinat/crystals/alcove_path.py.orig src/sage/combinat/crysta
          search algorithm.
  
          .. WARNING::
-diff -up src/sage/homology/homology_group.py.orig src/sage/homology/homology_group.py
---- src/sage/homology/homology_group.py.orig	2018-12-22 16:37:08.000000000 -0700
-+++ src/sage/homology/homology_group.py	2019-01-04 11:17:37.136047323 -0700
+--- src/sage/combinat/crystals/kirillov_reshetikhin.py.orig	2019-01-14 17:16:01.000000000 -0700
++++ src/sage/combinat/crystals/kirillov_reshetikhin.py	2019-02-07 15:44:37.612978369 -0700
+@@ -3443,7 +3443,7 @@ class CrystalOfTableaux_E7(CrystalOfTabl
+     <sage.combinat.crystals.kirillov_reshetikhin.KR_type_E7>` `B^{7,s}`.
+     """
+     def module_generator(self, shape):
+-        """
++        r"""
+         Return the module generator of ``self`` with shape ``shape``.
+ 
+         .. NOTE::
+@@ -3496,7 +3496,7 @@ class KR_type_E7(KirillovReshetikhinGene
+ 
+     @cached_method
+     def A7_decomposition(self):
+-        """
++        r"""
+         Return the decomposition of ``self`` into `A_7` highest
+         weight crystals.
+ 
+--- src/sage/groups/perm_gps/permgroup_named.py.orig	2019-01-14 17:16:02.000000000 -0700
++++ src/sage/groups/perm_gps/permgroup_named.py	2019-02-07 15:51:38.530055246 -0700
+@@ -3027,7 +3027,7 @@ class SuzukiGroup(PermutationGroup_uniqu
+         return "The Suzuki group over %s" % self.base_ring()
+ 
+ class ComplexReflectionGroup(PermutationGroup_unique):
+-    """
++    r"""
+     A finite complex reflection group as a permutation group.
+ 
+     We can realize `G(m,1,n)` as `m` copies of the symmetric group
+--- src/sage/homology/homology_group.py.orig	2019-01-14 17:16:03.000000000 -0700
++++ src/sage/homology/homology_group.py	2019-02-07 15:43:21.197614413 -0700
 @@ -109,7 +109,7 @@ class HomologyGroup_class(AdditiveAbelia
              sage: from sage.homology.homology_group import HomologyGroup
              sage: H = HomologyGroup(7, ZZ, [4,4,4,4,4,7,7])
@@ -22,10 +51,9 @@ diff -up src/sage/homology/homology_group.py.orig src/sage/homology/homology_gro
              sage: latex(HomologyGroup(6, ZZ))
              \ZZ^{6}
          """
-diff -up src/sage/rings/number_field/number_field.py.orig src/sage/rings/number_field/number_field.py
---- src/sage/rings/number_field/number_field.py.orig	2018-12-22 16:37:10.000000000 -0700
-+++ src/sage/rings/number_field/number_field.py	2019-01-08 16:25:39.730547708 -0700
-@@ -6613,7 +6613,7 @@ class NumberField_generic(WithEqualityBy
+--- src/sage/rings/number_field/number_field.py.orig	2019-01-14 17:16:04.000000000 -0700
++++ src/sage/rings/number_field/number_field.py	2019-02-07 15:43:21.220614222 -0700
+@@ -6622,7 +6622,7 @@ class NumberField_generic(WithEqualityBy
          return U
  
      def S_unit_solutions(self, S=[], prec=106, include_exponents=False, include_bound=False, proof=None):