feat: add default text font family and expose ENUM

[OrenMe]

Description of the Changes

add default text font-family to text style and expose the TextStyle on the player instance so ENUM is more accessible.

CheckLists

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• test are passing in local environment
• Travis tests are passing (or test results are not worse than on master branch :))
• Docs have been updated

[dvh91]

I wouldn't expose Roboto and other custom non-system fonts in the enum.
Maybe Hillel can assist with the font choice but I would go with:
'sans-serif' and 'serif'
other than that, the custom skin can define his own custom fonts and add it to the font options.