utils: remove unused import

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor party: move cola.dag components to cola.models and cola.widgets

This eliminates two files we have to open during startup.

Signed-off-by: David Aguilar <davvid@gmail.com>
grep: remember scrollbar and text cursor when refreshing

Signed-off-by: David Aguilar <davvid@gmail.com>
widgets.diff: remove unused import

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor: eliminate `cola.prefs` package

Move the git-config preference wrappers to cola.models.prefs.  Move the
GUI code to cola.widgets.prefs.  The common functionality, e.g.
diff_font(), moved to qtutils.

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor: eliminate cola.qt

Move the generally useful functions to qtutils.  Move ExpandableGroupBox
to widgets.archive where it is used.  Move QFlowLayoutWidget to
widgets.action where it is used.  Move the GitRefDialog and friends to
widgets.completion.

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor: eliminate the `cola.merge` package

Move widgets to widgets.merge and eliminate the package.  One less file
to stat during startup.

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor: eliminate cola.basecmd

Looking like a duck is enough; we don't need to derive (and keep an
entire module around) just for a single method.

Signed-off-by: David Aguilar <davvid@gmail.com>
refactor: move start_command(), run_command(), and fork() to core

Signed-off-by: David Aguilar <davvid@gmail.com>