Several changes and additions to platform agent framework

Various refactorings (mostly internal); code clean-ups; MONITORING state introduced; consistent use of a supporting NetworkDefinition object currently used to configure the platform agent while appropriate mechanism are defined; added commands CONNECT_INSTRUMENT, DISCONNECT_INSTRUMENT and GET_CONNECTED_INSTRUMENTS; renaming in CI-OMS interface to follow general CI coding guidelines; platform driver FSM introduced; added utilities to load networkDefinition from info provided by CI-OMS interface (used in various tests, including test_oms_launch2); preliminary checksum implementation and related platform agent command CHECK_SYNC. Also, for better naming consistency, renamed the RSN platform module and class as follows:
   ion.agents.platform.oms -> ion.agents.platform.rsn  
   ion.agents.platform.rsn.oms_platform_driver -> ion.agents.platform.rsn.rsn_platform_driver
   OmsPlatformDriver -> RsnPlatformDriver
So, per https://confluence.oceanobservatories.org/display/CIDev/Preload+development, I made a copy of the R2 Preload Resources spreadsheet, adjusted the PlatformAgent sheet to reflect the new pa/driver module and pa/driver class columns, and adjusted ion_loader.py accordingly.  

**NOTE**: Because of the above renaming in the RSN driver module and class, we will probably need to coordinate at the time of merging so a new copy of the original spreadsheet is used to reflect its most recent updates. Please let me know how you want to proceed.