Pull request wizard, fields sizes

Hi guys,

funny little annoying issue when ones has multiple repos and branches with long names with the same "root" (first part), which are automatically truncated in the edit box.

To check if branches are the correct tones, one needs to click on the drop down and check: it'd be great if you could extend the size of the combobox to the extend of the webpage.

In the end, there is a lot of unused space on the webpage....