implement new switch to deal with framing tags on TMX import

Implement the new api-switch defined in https://jira.translate5.net/browse/T5TMS-190 as GUI switch for the TMX-import.

The param is analogous to the translate5 config

runtimeOptions.import.xlf.ignoreFramingTags

and should point to it for more information (see tooltip).

It has the same values, as that system config: all, paired and none.

Label:

EN: Strip framing tags at import

DE: Umschließende Tags beim Import löschen

It should be placed as drop-down above the file field, where a TMX file can be selected for import (in the create new TM form and the "import to existing TM" form)

A tooltip of the new UI switch therefore should state:

• EN: Works analogous to system config runtimeOptions.import.xlf.ignoreFramingTags, but for TMX import. It strips all (or only paired) tags from the start and end of an imported segment, if activated. The system config should therefore have the same setting for the same client for to be imported tasks. If you need to convert exiting TMs, please ask the translate5 support for help.
• DE: Arbeitet analog zur Systemkonfiguration runtimeOptions.import.xlf.ignoreFramingTags, aber für TMX-Import. Sie entfernt alle (oder nur gepaarte) Tags vom Anfang und Ende eines importierten Segments, falls aktiviert. Die Systemkonfiguration sollte daher für denselben Kunden die gleiche Einstellung für zu importierende Aufgaben haben. Wenn Sie bestehende TMs konvertieren müssen, bitten Sie den translate5-Support um Hilfe.

Also the help text of the config

runtimeOptions.import.xlf.ignoreFramingTags

should be changed to the following:

If enabled framing tags (tag pairs only [setting: paired]or all tags [setting: all] that surround the complete segment) are ignored on task import. Does work for native file formats and standard xliff. Does not work for sdlxliff. See http://confluence.translate5.net/display/TFD/Xliff. If you change this setting, in many cases it might make sense to clean existing TMs. For this, the content protection feature, that supports TM conversion, can be used as a workaround. Please consult the translate5 support, if you need to clean existing TMs for help.
This setting correlates with the TMX import setting "Strip framing tags at import", that should be set to the same value.

Last but not least: Make the "t5 t5memory:migrate" command also be able to use the new param.