Move codes generating html file from xml files to SettingsLib (2/2)

LicenseHtmlGeneratorFromXml, LicenseHtmlLoader and indirecly AsyncLoader
shoud be commonly used by Settings and TvSettings.

So this CL will move them to SettingsLib.

Bug: 37763148
Test: building succeeded and tested on sailfish
  make ROBOTEST_FILTER=LicenseHtmlGeneratorFromXmlTest RunSettingsLibRoboTests
  make ROBOTEST_FILTER=LicenseHtmlLoaderTest RunSettingsLibRoboTests

Change-Id: I86b59d82c46b6c5f520a6be260363f1b6ffd43f4