Fixed coding style
Added reverse concatenation to concat in Metamorph

Introduced a new attribute called reverse for the concat-collector
in Metamorph which inverses the concatenation order if true. Instead
of appended values at the end of the output string they will be
prepended before the string.
Added module for grouping Pica multiscript fields.

This commit adds a new stream module which processes streams of Pica+
records with multiscript fields into a new structure which is easier to
process with Metamorph.

The new module is named `PicaMultiscriptRemodeler` and the corresponding
Flux module is called `remodel-pica-multiscript`.
Added new test case for `occurrence`-function.

The test case verifies that the `occurrence`-function in
method updates with each inner entity if sameEntity is set
and entities are nested.