Fix action invocation and registration

Fix action invocation and registration

Binding actions involving groupings are a bit more complicated when it
comes to DOM mapping. An instantiated Action can correspond to any
number of ActionEffectiveStatements, but we skimped that over and used
the SchemaPath (and after that, an invalid SchemaNodeIdentifier) to
identify them.

Correct this by requiring users to provide an ActionSpec, which is a
combination of an Action interface and a corresponding instantiation
path.

JIRA: MDSAL-712
Change-Id: I632c0f51b2e71fa1b0a04e43d5b1c50286430b21
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>