Rename mailparser to parsecontroller

* src/Makefile.am, src/mail.cpp, src/mail.h: Update accordingly.
* src/mailparser.cpp, src/mailparser.h,
src/parsecontroller.cpp, src/parsecontroller.h: Renamed.

The parsecontroller handles "reading" a MIME Mail but does
not do the actual MIME Parsing which now happens inside
the MIMEDataprovider. So the name should reflect that.