Implement Dynamic Attributes for SOP and PBS. Implement storage in SQLite
Add DAExampleModule to demonstrate dynamic attributes

This module demonstrates that we can add an arbitrary persisted value to SOP without any changes to core code.
Every time the object is moved, the move record is updated and the users in the scene alerted
The number of moves is persisted over server restarts in sqlite
Implement dynamic attribute persistence on mysql and mssql

mssql is untested
Encapsulate an OSDMap in DAMap (was DynAttrsOSDMap) rather than inheriting from it

This is the easier way to give us control over locking, rather than asking that OSDMap IDictionary methods be virtual
Lock DAMap rather than encapsulated OSDMap

This allows external lockers to preserve atomicity of dynamic attribute changes
Added missing DynAttrs references in MySQL
Changed DAMap to be the container of "data stores", which are OSDMaps. Store names must have at least 4 characters.
Stopped storing dynamic attributes in the PrimShape
Store NULL in the 'DynAttrs' column if the prim doesn't have any dynamic attributes
Added DynAttrs to the serialized XML format of prims. When copying prims, use deep copy for DynAttrs.
Disabled DAExampleModule
Added unit tests for Dynamic Attributes
Fix tests by adding DynAttrs add column commands to RegionStore.migrations (these were originally in 021_RegionStore.sql which I might have forgotton to add 2 years ago).
Remove the accidental PrimShapes column that I added back to the SQLite region store
Merge branch 'dynamic-attributes2'