start time introduced for UserTalk
mail-service introduced
email service implemented
bugfixing gmail
Merge remote-tracking branch 'origin/develop' into feature/gzi/server

Conflicts:
	server/conferencebuddy-web/src/main/java/ch/sbb/conferencebuddy/UserResource.java
gzi: gmail credentials moved into a property-file
gzi retry-count for sending email introduced, rating bug fixed
Merge branch 'develop' into feature/gzi/server
gzi: pid type changed from long to string
gzi: timestamp mapping to JSON fixed
Merge pull request #99 from SchweizerischeBundesbahnen/feature/gzi/server

Feature/gzi/server