Implement font-family dropdown

This issue has been migrated from mozilla/webmaker-android#1750.

It was originally written by flukeout on Sun May 10 2015 and had the following description:

• It's got too much left padding
• Doesn't have a little arrow indicator on the right side
• The dropdown options don't use the corresponding fonts to display the names
• The dropdown has radio buttons as the selection metaphor

Compare to spec below (and next page showing dropdown treatment and selected state) https://projects.invisionapp.com/share/BK2M18Q28#/screens/72332476?maintainScrollPosition=false

On Mon May 11 2015, thisandagain commented:

**@**vazquez Can you please drop in a reference PNG and link to sketch file?

On Tue May 12 2015, vazquez commented:

Design Documentation

Text Attributes Screen

Text Dropdown Sketch File

https://www.dropbox.com/s/8px5x6vx4o20psc/Text%20Dropdown.sketch?dl=0

Notes

• The Font Family selector acts as a Material Design dropdown list. It's pretty much the same as a normal dropdown except it looks just a little bit different.
• The user has the freedom to select the text to be bold AND italicized AND underlined.
• The user can only select one text alignment property. As an example, the text cannot be left aligned AND right aligned.
• Selected states for Text Style and Text Alignment is represented by a blue 'active state', as shown below.

Text Options with Dropdown selected

• Every font shown here is accessible through Google Fonts.

On Wed Jun 03 2015, Pomax commented:

This issue is going to need more work after beta, because we can't style option elements inside select dropdowns in WebView. mozilla/webmaker-android#2076 at least adds in the actual fonts we make use of, but we may need to find, or roll our own, a different way to present a dropdown menu.