Multistep pages should have the possibility to add additional submit btns

refs #6136
Multistep page names should not be set implicitly on instantiation

refs #6136
Add placeholders for our wizard pages

refs #6136
Fix that Form::reset() does not clear sub forms as well
Multistep page configurations need not to be writable

refs #6136
Add wizard step to show and check requirements

resolves #6139
Add token authentication to the installation wizard

resolves #6135
Update Icinga 2 version in the Puppet manifest

fixes #6219
Documentation: Fix missing preferences*,sql

fixes #6243
Web\Form: Revert "Fix subForm functionality"

This reverts commit 51bac035ac1bdee2c63f680ec66120beb1081af3.
The div element introduced by this commit breaks inline form layout
IDO Queries: performance quickfixes

Will be obsoleted by the new filter implementation, but for now it
helps a little bit
list/services: ignore broken service image hacks

People used to configure something like "dot.png'> <img ..." as their
service image icon. Those hacks will no longer work as we correctly
escape everything. This fix hinders Icingaweb from even trying to load
them.
ErrorController: show valid title for exceptions

Multiline strings are not considered being a valid title. This patch
strips all but the first line from the exception message when setting
the title attribute.
Web\Url: add a shift() method

This methods allows to retrieve an URL param while removing it from the
URL object
show/services: don't navigate to the right

When using list/services for show/services (services for a single host)
we us an ugly PREG-based hack fixing the base link target. This got
broken by the multiselect feature, now it's working again. We need a
better solution for this.
ShowController: don't show a random service

When you chose a host and clicked on "Services" the GUI used to show
a random (the first) service. Made no sense, should work as expected
right now.
css/tabs: waste less space for dropdown

Dropdown arrow is smaller right now and is slightly rounded like the
other tabs are.
js/ui: remove hardcoded/duplicated with/height
js/events: do temporarily not respect tab focus

This has been added for keyboard navigation but caused some trouble.
Postponed for now.
js/events: improve search field change detection

This used to be nasty since "search" is the field with the initial
focus. Right now we detect "real" changes, this might be implemented
in a more generic way for all autocompleting fields later on.