Add options to mask values based on inclusion list instead of exclusion list

[vincent-psarga]

Currently, the options to handle privacy are based on an exclusion list. This does not work fine for our use-case. The idea behind this pull request is to anonymize everything by default and allow the end user to specify which part of the recorded app should not be anonymized.

It would look something like this for example:

record({
  maskTextExcludeSelector: 'header, footer, nav.menu'
})

With such configuration, all content of the web page would be anonymized except for the header, footer and main navigation.

It also adds the possibility to have some text not masked inside a masked block.