Qt: Add support for EncryptJobs with generic flags
* lang/qt/src/encryptjob.h, lang/qt/src/signencryptjob.h, lang/qt/src/qgpgmeencryptjob.h, lang/qt/src/qgpgmeencryptjob.cpp, lang/qt/src/qgpgmesignencryptjob.cpp, lang/qt/src/qgpgmeencryptjob.cpp: Add start and exec overloads that accept generic EncryptFlags.
While this technically is an ABI break (vtable change) there
are no known classes outside qgpgme that inherit encryptjob
or signencryptjob. And the new functions should be added
to the bottom of the vtable.