Rework to use launcher wrapper from libqtappfw

Rework to use launcher wrapper from libqtappfw

Changes:
- Switch to using the new app launcher API wrapper from libqtappfw
  in order to migrate to the new gRPC based API implementation.
- The appStarted and appTerminated methods in HomescreenHandler have
  been renamed to activateApp and deactivateApp, respectively, to
  better reflect what they do.  A new processAppStatusEvent method
  had been added that calls them as appropriate based on the event
  from the AppLauncherClient status update signal.
- The copyright headers in the source files have been tweaked to
  remove the Apache license boilerplate in favour of a SPDX license
  tag.
- The code in main.cpp that was not formatted with Linux-style has
  been reformatted to match the rest of the file.

Bug-AGL: SPEC-4559

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I236cb6a412945a6df7d35652c55f664264964f9c
(cherry picked from commit 20f629dd6d8628611d950073c4f7a0446c40365a)