Previously relationships defiend as many_many came in a special type
of RelationList - however now this can be one of two types of
RelationList depending on the type of definition, with both being
valid many_many relationships.
This had the unfortunate side effect of seeing the OrderableRows
component in (the least) cease functioning correctly. No longer.
This also has the fortunate bonus of allowing a many_many relationship to
be versioned; where previously while each item in the relationship could
be versioned, the relationship itself could not.
* Fixed GridFieldOrderableRows issue when data class is Versioned and relation is has_many
* just compare table names rather than updating existing getSortTable() func
* Initialising button before attempting to enable or disable it
* Updating class reference
* Adding exception use case
* Removing unused use case
* Including Exception class for classes where exception is used.
