Add option to whitelist domain from containment

[sents]

This pull request adds an option to include a list of whitelisted domains.
It is my first real pull request so I hope I am doing this right.

Note that this would fix #104.

[Perflyst]

Thanks! I will test your patch as soon as possible. Also it needs a quick rebase

@hackerncoder what do you think?

[sents]

I rebased it now.

I've noticed that pressing enter in the extension preferences triggers saving the preferences.
As the domains are separated by newlines there is no way to enter multiple domains right now.
I would propose to use "," or ";" as separator. Both characters are not allowed as part of domain names.

[sents]

The whitelist option uses a textarea element now, so it is possible to enter multiple domains.

[hackerncoder]

Thanks! I will test your patch as soon as possible. Also it needs a quick rebase

@hackerncoder what do you think?

This is some serious code, and somewhat out of my ballpark (especially since I don't have that much energy right now), but seems fine.

[hackerncoder]

I tried it a little (google.com and blogger.com) and it seems fine.

[Perflyst]

@sents after hackerncoder's test I merged and released this feature. the containment is broken if the whitelisted google urls are empty -> by default the containment is broken

[Perflyst]

Additionally your popup is broken if the preferences are saved with empty whitelist

[hackerncoder]

the containment is broken if the whitelisted google urls are empty -> by default the containment is broken

I can't reproduce this.

[sents]

I'll look into it today.

[sents]

Unfortunately I am not able to reproduce the bugs relating to the empty whitelist. I've tried my standard profile and a fresh profile without any other extensions.

[Perflyst]

In case you downloaded from AMO - I disabled version 1.5.2 there. If you download https://github.com/containers-everywhere/contain-google/releases/download/1.5.2/google_container-1.5.2.zip, create a fresh profile, use debug addons -> load temporary addon you should be able to reproduce it.

[sents]

I installed it on a different computer with Firefox 82 and could reproduce the bug. For some reason whitespace gets inserted into the setting when loading the settings for the first time. Thank you for your tip! I will now look into this.

[sents]

After the fix of #109 leaving the whitelist empty doesn't cause any problems anymore.
The problem was caused by the variables relating to whitelist being undefined, when loading the extension for the first time.
The checkboxes are also undefined, but this doesn't cause any problems because undefined works with boolean operators.