Add code-completion for SpringStandard dialect (th:field and th:errors)

[rreimann]

Currently there seems to be no code-completion support for the SpringStandard dialect, containing th:field and th:errors.

I would appreciate if code-completion for SpringStandard could be added.

[ultraq]

Of course - I can't believe I forgot about the Spring dialect!

[ultraq]

Checked-in code that adds support for the SpringStandard dialect. Will be a part of the next release.