Use mt() in the monitoring module instead of just t()

fixes #7330
LDAP Auth: Make group loading really optional

fixes #7432
logging: Fix that setting a numeric log level is flawed
PHP: avoid short tags <?
Command transport: Show helpful exception messages

refs #7437
Fix CSS syntax errors
monitoring: Remove 'Remote' prefix from the remote instance form elements' labels

The 'Remote' prefix of the remote instance form elements' labels is superfluous because the
instance's type already tells that it's remote.
monitoring: Rename label of the path to the local Icinga command file

Rename 'Local filepath' to 'Command file' because the remote instance form is using 'Command file' too.
monitoring: Translate headings in the config overview
monitoring: Don't translate exception messages in the local command file
monitoring: Don't translate exception messages in the remote command file
monitoring: indent php blocks in config/index.phtml properly
monitoring: throw meaningful logic exceptions in the command file classes
monitoring: Write transport directive to instances INI configuration

Further I replaced if-elseif blocks w/ switch when branching based on the value of a single parameter,
which would have to be implied otherwise by looking at all the conditions.
monitoring: Rewrite Service::getStateText() to get the optional translated textual representation of a service state
monitoring: Remove unnecessary break after throwing an exception
Auth: Remove setting the not existent layout 'login' when logging out externally authenticated users

fixes #7191
Logger: Fix level comparison
Merge branch 'master' into feature/deduplicate-puppet-code-6842