lib: Add NonEmptyFileIterator

Add iterator for iterating over non-empty files.
lib: Add FileExtensionFilterIterator

Add iterator for iterating over files having a specific file extension.
doc: Use Icinga Web 2's iterators
doc: Remove iterators because they are superseded by iterators from Icinga Web 2's library
doc: Make path to Icinga Web 2's doc configureable

refs #7196
doc/configuration.php: Prefer @type over @var
doc/run.php: Remove superfluous newline
monitoring/configuration.php: Prefer @type over @var
doc: Set version to 2.0.0
doc: Use sprintf for "Missing parameter x" exceptions
doc/parser: Fix PHPDoc indentation
doc/Controller: Do not use 'void' results
doc: Throw an exception if Icinga Web 2's documentation is not avaiable

refs #7196
doc/IcingawebController: Use sprintf for "Missing parameter x" exceptions
doc/IcingawebController: Do not use 'void' results
doc: Make path to module documentations configureable

refs #7196
doc/ModuleController: Do not use 'void' results
doc: Prefer "root" doc path over configured path

If the "root" doc path, i.e. application/doc exists, it is preferred over the configured
one.

refs #4075
doc: Add module documentation
doc: Add module config.ini for packaging

resolves #7196