feat(developer): add web font references to package

While a package supports a .ttf or .otf font for the OSK and Display
fonts for use within the Keyman apps, on websites it also supports .woff
and .woff2. This change makes it possible to specify a set of fonts for
a package which will be provided through api.keyman.com to websites.

This means that .woff and .woff2 fonts may also be included in the
package and may not be used on target devices at this time, it further
opens the pathway to deploying .kmp packages to web in the future.

The deployment stage of keymanapp/keyboards will require a new phase to
copy web fonts from packages to s.keyman.com.