Error handling for get_tag

[fkiraly]

This adds the possibility to raise an error when get_tag is used.

An error will always be raised if the function is used with parameter defaults and the tag with the specified tag_name does not exist, but this can be overridden by setting the new raise_error parameter to False.

This should hopefully prevent the human error that caused the bug in #1449 for the future.

FYI @aiwalter, @thayeylolu, @mloning

This PR also contains a second test for get_tag to cover the behaviour if raise_error=True, the old test covers the behaviour if raise_errpr=False with minor changes.

The change has caught the following bugs which are also fixed:

• "enforce_index_type" tag was sometimes written "enforce-index-type", this was changed to "enforce_index_type" consistently
• transformer base class did not have any default tag values set, which caused framework to look for non-existent tags - added a set of defaults
• "coerce-X-to-pandas" was called in some classifiers but not set in the tine series classification base class

[fkiraly]

@aiwalter, do you understand why this is not failling the tests you fixed in #1449? I'm surprised that it doesn't.

[fkiraly]

found it, forgot the raise in front of ValueError.