Exception messages should be single-line strings

fixes #6095
Fix filter test location
Rewrite perfdata plugin classes

refs #5973
Fix usages of Icinga\Module\Monitoring\Plugin\*

refs #5973
Fix cli default log configuration and js-loader debug message
Merge branch 'bugfix/failsafe-perfdata-parser-5973'

fixes #5973
Fix division by zero in Icinga\Util\Format

refs #6125
Fix inline pie reload.

refs #6124
Do not change browser title on autorefresh

fixes #6168
Move hover menu downward

fixes #6169
Upgrade JShrink to 1.0

refs #6165
Upgrade htmlpurifier to 4.6.0

refs #6165
Upgrade lessphp

* Upgrade from 0.3.9 to 0.4.0
* Document package source
* Remove overhead

refs #6165
refs #6166
Put focus into search field on initial page load

fixes #6170
Detect and handle remote links

Currently they trigger XHR requests if not given a special target.

fixes #6159
Completely ignore remote links

There are no issues with "returning true" so this should be the
preferred way. No need to fall back on "window.open" here.

fixes #6159
Initial "click" handling for dropdown tabs

Still uncomplete, there are a number of edge cases that need to be
handled. Keyboard navigation is one of them, hover/click distinction
is another one.

refs #6167
Improve console log message on errors like 404

Former '404 Not found' plus weird HTML snippet is now: '404 Not Found:
 Page not found. Enabling the "bpapp" module might help!'
Restore click behaviour for table links and rows

Multiselect handlers should influence only multiselect tables. Still
unhappy with current behaviour, but links should work fine right now.

refs #6162
Upgrade Parsedown to 1.0.0-rc.4

Please note that this invalidates my img size patch, I forgot to bring
it upstream. Still TBD.

refs #6165