Use If-Modified-Since and catch 304-Not-Modified in API Queries. Resolve #121
use Last-Modified from API response instead of locally calculated time
Merge branch 'master' into http-304

Conflicts:
	android/src/main/java/com/thebluealliance/androidclient/datafeed/Database.java
Merge pull request #123 from phil-lopreiato/http-304

Use 304-Not-Modified