Add file list buffer to reduce Gerrit calls

Change-Id: I5c0bd4bab669eade1d279d3573ed663825102f5e
Split Decorator and PostJob plugins

- ReviewHolder is a singleton used to share ReviewInput between
 GerritDecorator and GerritPostJob
- HashMaps have been changed to ConcurrentHashMap in ReviewInput to handle
 hypothetical concurrent access from GerritDecorator and GerritPostJob

Change-Id: I8f2cadda7b74da91fb784b35bb6279385f2278a4
Add initializer for configuration setup

Change-Id: Ic57e66ba18a8ed7a73cb86e96dda163c1dce69f9
Facade returns an unmodifiableMap.

Change-Id: I3897a039384f5ea671110f189b0bdec9c09e4c20
Removed unnecessary proeprties in plugin definition.
These properties are retrieved through Settings as being declared with -D on call.

Change-Id: I368a803183036c1e2529ef307844aa6f1805deca
Merge pull request #2 from mildis/split-plugin

Split plugin