#2 Make pull functionality for active branch

**As a user I want to have button to fetch and merge change for active branch** * Add "Pull" button to top bar when * "Pull" button should be active only when repository is selected and stays on branch * "Pull" button should open "ok/cancel" dialogue with 2 options of pull strategies: 1. rebase(default) 2. merge * While pull operation main window should be dimmed

https://git.semlanik.org/semlanik/CuteGit/commit/28804afe7b695f3da9ca436b87992f6b7509df0c

https://git.semlanik.org/semlanik/CuteGit/commit/45f4de42f022c65300342b676ac587308d75a525

https://git.semlanik.org/semlanik/CuteGit/commit/8e6d9e82abd2dd83d0eea961d85f617510d3fc53