Rocket Jira: Improve changing preferences

[deftbrain]

The Rocket Jira userscript uses the GM_Config library for managing preferences. The library provides nothing for working with dependent fields. Due to this reason we have to do a lot tricks in code and click the Save button in the Preferences modal window every time when we need to display a dependent field once a dependency field is set. It is very annoying so we should replace the GM_Config library with our own modal window (example of the implementation). This will help to simplify code and improve UX.