widgets.completion: fix GitRefLineEdit construction

The first argument is the hint text, so remove `self` since
it's not needed and shoudl have been written `parent=self`.

Signed-off-by: David Aguilar <davvid@gmail.com>
git-cola: avoid unicode u'' in help message

Cast to str() to prevent python2 from print u'' strings in the usage.

Signed-off-by: David Aguilar <davvid@gmail.com>
qtutils: make icon() more robust

We never see str() but we it's better to be safe.

Signed-off-by: David Aguilar <davvid@gmail.com>
qtutils: teach box() to handle layouts and spacing

Signed-off-by: David Aguilar <davvid@gmail.com>
qtutils: add form(), splitter(), and grid()

Add helper functions for creating forms, splitters, and grid layouts.

Signed-off-by: David Aguilar <davvid@gmail.com>
widgets: use qtutils' hbox(), vbox(), grid(), splitter(), and form()

The diffstat says it all:

27 files changed, 454 insertions(+), 790 deletions(-)

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