CORE-4126 Added a few resource strings 

In particular, the following string were added.

* the system messages action menu item label
* the system message arrival announcement message
* the system message announcement link label
IN PROGRESS - issue CORE-4126: Add system notification display area to
DE. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4126

Added message indicating that there are no system messages available.
IN PROGRESS - issue CORE-4170: Add announcement feature to the DE. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4170

Externalized the announcer widget styling
IN PROGRESS - issue CORE-4170: Add announcement feature to the DE. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4170

Modified the styling of the announcer panel styling to better
distinguish the top panel when there are multiple messages.
IN PROGRESS - issue CORE-4170: Add announcement feature to the DE. 
https://pods.iplantcollaborative.org/jira/browse/CORE-4170