infrastructure for fetching packrat-extended package info
Merge remote-tracking branch 'origin/master' into packrat-packages-pane

Conflicts:
	src/gwt/src/org/rstudio/studio/client/server/remote/RemoteServer.java
create context-appropriate packages table for packrat mode
when packrat mode is on, call packrat for extended package info
show packrat-specific columns when packrat mode is on
improve package library detection; hide manipulate and rstudio
add tracing for hash checks (in preparation for snapshotting)
Merge pull request #114 from rstudio/packrat-packages-pane

Package pane improvements for Packrat