Add SearchParameters

Added a new Data class SearchParameters (used to be FACTFinder_Parameters)
which represents all parameters relevant for the actual search. Currently,
this is intended for read-only purposes.
Also, the RequestParser can now return both processed and unprocessed
parameters, although we will usually use the processed ones.
Merge branch 'development' into release
Update changelog
Update documentation for release 1.0.0-beta.2