Changed project graph to latest month

The small project graph now displays data for the
last 30 days instead of last 24 hours.

Change-Id: I3ac82d29b32e3c701a792efa284b5c8d7ef3fab4
Changed default implemetations for statistics fetching

Modified default implementations of statistics fetching
to return empty lists/maps instead of null.
By doing this, the user will see empty graphs (no data) instead
of broken links when using a custom knowledgebase without full
statistics support.

Change-Id: I321ae3dc366253427b252a59c04e5e41d2f07930
Added info text about delayed graphs

There is now a small info text on the bottom of the global graphs
page, stating that graphs are delayed up to the specified cache
expiration time.

Change-Id: I18d8de9c91ee76202778368f29994ef5f747dd6c
Invalidating all project graphs after build

All graphs belonging to a specific project are now
being refreshed after each time that project has
been built.

Change-Id: I43dae03b3db565feab5122f72e9c96dbe2a98395
Merge "Changed default implemetations for statistics fetching" into internal
Merge "Added info text about delayed graphs" into internal
Merge commit 'refs/changes/79/677979/3' of build-failure-analyzer

Conflicts:
	src/main/java/com/sonyericsson/jenkins/plugins/bfa/graphs/GraphCache.java
Invalidating all node graphs after build

All graphs belonging to a specific node are now
being refreshed after each time that node has
built a project.

Change-Id: Ie0ca558a2f25fae53485eab2804d56dd2f50442a