Refactoring of the project and new options added

[elchininet]

This pull request refactors the code to make it easier to add new styles and to extend the functionality of the library, making the code more readable and avoiding unwanted mistakes during styles coding.

As part of this pull request new options have been added to the library, allowing one to hide elements from the overflow menu on the top right corner. It also implements a better way to hide the Search and the Assistant buttons, so, if these options are used, it will also affect these buttons when they are inside the top right overflow menu on small screens.

Option	Hides
hide_search	Hides the search button on the top menu and inside the overflow menu on small screens
hide_assistant	Hides the assistant button on the top menu and inside the overflow menu on small screens
hide_edit_dashboard	Hides the "Edit dashboard" button inside the overflow menu
hide_refresh	Hides the "Refresh" button inside the overflow menu in lovelace yaml mode
hide_unused_entities	Hides the "Unused entities" button inside the overflow menu in lovelace yaml mode
hide_reload_resources	Hides the "Reload resources" button inside the overflow menu in lovelace yaml mode

If some of these options are used in a way that the overflow menu ends up empty, it will hide (same as using the option hide_overflow).

Closes #14

Note: this pull request depends on #25, it contains the same changes contained in the aforementioned pull request. After #25 gets merged, this branch should be rebased to keep only the changes relatives to the new features introduced here.

[elchininet]

@NemesisRE, this one is ready. It is better to wait for the last pull request to make a release with all the changes.
If new versions pop up people will think that it is the version that fixes Home Assistant compatibilities.

[NemesisRE]

alright sounds good then we wait for #28 to be ready and merge them both at once as version 1.9 or so

[elchininet]

@NemesisRE,
Yes, that would be the best approach.
Did you check this one, it implements a lot of features. Can I merge it?

[NemesisRE]

The features looked good for me