Bump version to 0.6
SettingsDialog: Remove  obsolete options

Namely search-show-retweets which just sucks and upload-provider which
only ever had one option
SettingsDialog: Move everyhing into a GtkStack

... and use a GtkStackSwitcher to switch between pages.
Let's see how that works out.
Merge branch 'master' of https://github.com/baedert/corebird
Merge branch 'master' of https://github.com/baedert/corebird
resources: Remove connection-lost-dialog
SettingsDialog: Set the type hint to DIALOG

... and add adjustment1 back so Gtk+ does not complain.