create store for orderparameters
more cleanup for op storage
Implemented PathReversal and ReplicaExchangeMove
Added GlobalState class
Fixed more on OrderParameter storage
Changed snapshot behaviour to be stored separately
fixed errors in storage simplification
Merge branch 'master' of github.com:choderalab/msm-tis into snapshotchange

Conflicts:
	opentis/snapshot.py
Fixed sandbox and Simulator to run with new OpenMM Simulator object
Fixed showtree.py for new storage
Fixed showtree.py plot range
minor improvesments on globalstate
Added GlobalState with showtree support
fixed horizontal shift error in showtree
Possible fix for velocity-less trajectories.
Fix to run sandbox w/ md engine abstraction layer
Merge pull request #1 from dwhswenson/pr0049

Possible fix for velocity-less trajectories
added generic return of 'None' for all load functions if idx < 0
added generic return of 'None' for all load functions if idx < 0
added generic return of 'None' for all load functions if idx < 0
Merge pull request #49 from jhprinz/master

Overhaul of storage with improved order parameter support, as well as support (for all functions) for "None" if idx<0