Allow more customization on the default toggle system

Allow more customization on the default toggle system

The naming convention remains unchainched. Default toggles are added if no mw-collapsible-toggle child element is present. Premade toggles have already one ore more mw-collapsible-toggle elements defined.

Default and premade toggles (mw-collapsible-toggle) still cannot be mixed/combined with remote toggles (mw-customtoggle).

* The default toggle got less rigid by removing dependency on <a> elements.
* Support for multiple premade toggles was introduced.
* The expand/collapse messages can be used by premade toggles via mw-collapsible-text.
* Removed the linksPassthru option. This step allowed merging premadeToggleHandler into actionHandler.
* The pass through functionality is now applied to all <a> elements since the default toggle does no longer depends on those.
* Removed mw-collapsible-bracket because it was not used and is deprecated by mw-collapsible-text.
* The test suite was adapted to reflect the latest changes.

Change-Id: Ic8627c4c185e8e4175e6fef1c8e1c2190e54edaa