TabUI collapsing/expanding improvements

[skoudoro]

this PR solves #776:

• it provides a parameter to initialize it collapsed for some applications.
• it allows to collapse/expand by single clicking on the active tab.

@guaje, can you test this branch and let me know if it is ok for you? thanks

[guaje]

Great! Thanks, @skoudoro. This solves the issue. Should I go ahead and merge it, or do you plan to add any changes to it?

[skoudoro]

You can go ahead and merge it @guaje

[guaje]

You can go ahead and merge it @guaje

Great! Merging.