Draft: Implement override for `text` property

[betalars]

This implements #2

To prevent a merge conflict in _update(), it also includes changes made in #18

I am using the _set() and _get() methods to change the behavior of the text variable in the super class.

Please consider this to be a draft, because I have not tested this a lot.

Additional Notes

~~I have tried to remove the markdown_text property as this change makes it somewhat redundant. However in testing it did not really work and things got tangled up. I think it had something to do with the inspector calling get text, but honestly I would need to look further into it.~~

Update: I actually managed to remove [markdown_text]. But I honestly it is kind of redundant because I still need the [_original_text]

~~It may also just not be worth the effort honestly.~~ You can revert the last two commits if you don't like it.

~~However if you want to remove markdown_text, you should add it as a virtual property by overriding get_property_list and adding it to the set function so users that update this AddOn won't lose all their markdown texts. (see the review)~~ ~> I have made this would not be a breaking change.

[betalars]

I made some changes to this PR that would also gracefully deprecate the markdown_text property without causing breaking changes.

I think it may remove some amount of confusion, but it also adds some. I don't know. You can choose.

[daenvil]

Thank you! i'll take a look when i get a chance

[betalars]

Yeah no hurries. Mainly needed the translation support for myself and decided to share it with others. This PR is mainly a gesture of gratitude, so don't stress yourself to get to it.