[TabWidget] Make sure current tab is loaded on session restore

Fixes issue with current tab not being loaded on session restore
with "don't load tabs until selected" option.
It was needed to switch to other tab and then switch back to first tab
to actually load it.

Also pause updates of the whole browser window when restoring session.
[Build] Fix building with Qt 4.7
[Click2Flash] Fix playing YouTube videos with Qt5

Closes #1283