This commit allows chaning default branch update style through global
and repository settings. The setting affects "Update branch" button
in PR view (button shows when some commits are ahead of master branch).
When default update style is set to "rebase", dropdown button updates branch
by rebase by default. When update style is set to other value, dropdown button
updates branch by merge. Any of these actions may be selected using dropdown
in any case.
Signed-off-by: George Bartolomey <george@bh4.ru>
13ca6c14f1