Factor out all text layout from TextField into TextFieldContent

This will make moving layout to a rendering backend on another thread much easier
Merge pull request #1088 from tschneidereit/master

Factor out all text layout from TextField into TextFieldContent
Lazy initialization of AddonManager; async getVersionInfo()
Merge pull request #1089 from yurydelendik/lazy-version

Lazy initialization of AddonManager; async getVersionInfo()