[TASK] Ensure type of Dynamic fields

The current solr version rejects indexing if the
types of the dynamic fields do not match. As TypoScript
is solely "text-based" an _intS field for example may be
filled with '' which then prevents indexing.

This changeset adds a basic type-converter for dynamic
fields from TypoScript.

Change-Id: I264940b2a6e557ef8af95745d5724c0fed4685fe
Releases: 3.0
Reviewed-on: https://review.typo3.org/27678
Reviewed-by: Olivier Dobberkau
Tested-by: Olivier Dobberkau