add MongoTx annotation to make sure, that read operations are also done on the primary mongodb server
add MongoTx as well to FileStorageService to avoid strange AspectJ problem

Conflicts:
	src/main/java/de/is24/infrastructure/gridfs/http/storage/FileStorageService.java
bugfix for mongo tx aspect being applied to proxy classes

Conflicts:
	src/main/java/de/is24/infrastructure/gridfs/http/storage/FileStorageService.java