Add support for imports from qgis.PyQt

this adds support to imports from the qgis.PyQt packages like
from qgis.PyQt.QtGui import (QCheckBox, QIcon)

this kind of imports are already used by some plugins
without having the PyQt5 structure of packages (i.e. they use
from qgis.PyQt.QtGui import (QCheckBox, QIcon) instead of
from qgis.PyQt.QtGui import (QIcon)
from qgis.PyQt.QtWidgets import (QCheckBox)

scripts/qgis_fixes/fix_pyqt.py

@@ -7,7 +7,7 @@
 from lib2to3.fixes.fix_imports import alternates, FixImports
 from lib2to3 import fixer_base
 from lib2to3.fixer_util import (Name, Comma, FromImport, Newline,
-                                find_indentation, Node, syms)
+                                find_indentation, Node, syms, Leaf)
 
 MAPPING = {
     "PyQt4.QtGui": [
@@ -382,6 +382,15 @@
 }
 
 
+new_mappings = {}
+for key, value in MAPPING.items():
+    match_str = key.replace('PyQt4', '')
+    match_str = '{}{}'.format('qgis.PyQt', match_str)
+    new_mappings[match_str] = value
+
+MAPPING.update(new_mappings)
+
+
 def build_pattern():
     bare = set()
     for old_module, changes in list(MAPPING.items()):
@@ -391,10 +400,14 @@ def build_pattern():
 
             if '.' not in old_module:
                 from_name = "%r" % old_module
+
             else:
                 dotted = old_module.split('.')
-                assert len(dotted) == 2
-                from_name = "dotted_name<%r '.' %r>" % (dotted[0], dotted[1])
+                if len(dotted) == 3:
+                    from_name = "dotted_name<%r '.' %r '.' %r>" % (dotted[0], dotted[1], dotted[2])
+                else:
+                    assert len(dotted) == 2
+                    from_name = "dotted_name<%r '.' %r>" % (dotted[0], dotted[1])
 
             yield """import_name< 'import' (module=%s
                                   | dotted_as_names< any* module=%s any* >) >