Implement adding secrets to vault from UI

[Kamilcuk]

Try to implement #22 .

I needed/wanted to refactor a lot to have common code paths instead of separate. The frivolous usage of global namespace and pollution of symbols will bite in the long run. I added some comments, but the code is anyway a long way from mediocre.

I added "add" page for adding passwords from the ui. The fields is filled with the first matched pattern and secrets group to ease up filling. I use only a single secrets group.

This requires testing if it works correctly for all users, if errors are properly handled. Also needs to be tested with multiple secrets directory, I use only one. Thanks.

[mulbc]

Thanks for investing effort to refactor and improve the code. If possible, please split your work into one PR that refactors and then a second PR that adds functionality. That way it's much easier for me to review