Tentative first crack at separating archving stuff into a base class and RAMP-specific class.
Second round of refactoring changes to separate RAMP stuff from base. Still doesn't build.

--HG--
extra : rebase_source : 8f4d2169eae743b43f9d1d749bfd17cb66a41276
Completed initial re-factoring to prepare for alternative types of archiving.

--HG--
rename : SIL.Archiving.Tests/ArchivingDlgViewModelTests.cs => SIL.Archiving.Tests/RampArchivingDlgViewModelTests.cs
extra : rebase_source : 17e2270cea19dea3bf435b98a0ce9b41fb4ffe26
Oops. This file is needed, too.