move Tab toggle button creation to registry

Add toggle property to Tab storing each tabs toggle button.
This way we are able to mark them as active when opening and
deactivating them again upon closing of a tab.

TabRegistry module now does create toggle buttons in
TabRegistry#createToggleFor.
Code was unnecessarily split up in two modules. Now the complete button
is handed over to the Tab for it to act upon it.

Remove unused method TabRegistry#open.

Change console.log to console.debug to less spam console output.
Mark active Tab toggles with upward triangle
move controlbar SCSS vars
Merge pull request #198 from line-o/active-tab-button

Active tab button