Moving sources to src part 1: Move files.

This only move files without adjusting any paths.

This moves:
- lib/quick -> src/webengine/api (API files)
  lib/quick -> src/webengine (other files)
  This contains the main QtWebEngine module library since
  <ec7b2ee70a8b2db7fb87f50671a001ddd54697b0>.
- lib/widgets -> src/webenginewidgets
  Also rename this directory to match its module name and rename Api to api.
- lib -> src/core
- process -> src/process
- resources -> src/core/resources
- tools/* -> tools/scripts/

The build directory is spread as follow:
- build/build.pro -> src/core/gyp_run.pro
- build/qmake_extras/* -> src/core/ (for the host and target .pro files)
- build/qmake -> tools/qmake
- Build related scripts -> tools/buildscripts

Change-Id: I0cded1de772c99c0c1da6536c9afea353236b4a1
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>
Reviewed-by: Andras Becsi <andras.becsi@digia.com>
Moving sources to src part 2: Adjust paths.

NOTE: To build after this you should rerun init-repository.py or run
$> git submodule sync
$> git submodule update
$> git config qtwebengine.chromiumsrcdir src/3rdparty

This makes everything build by adjusting paths.

Other mixed-in changes:
- Rename qtwebengine_src variables in scripts to qtwebengine_root to
  avoid confusion.
- Cleanup the release and debug extra targets that were in lib.pro.
  This file has also been split into src.pro and core.pro.

Change-Id: Ieee9158a65f526b15244eaca59e779b7069d337e
Reviewed-by: Zeno Albisser <zeno.albisser@digia.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>