Adding -Werror compilation flag

Adding -Werror compilation flag

[Issue#]   N/A
[Problem]  Compilation warnings being ignored by developers
[Cause]    Too much compiler output
[Solution] Adding a -Werror compilation flag so that warnings are treated as
           errors
[Verify]   Check that the project builds without warnings

Compilation warnings should not be ignored. They often warn about things that
may cause trouble if unattended. Too much warnings also pollutes the compiler
output making it illegible.
Adding this compilation flag will allow us to maintain the quality of our code.

Note: This commit also fixes one warning in WebKitEngineService.cpp
(initialization list reordering).

Change-Id: If30512b534268d5857ec08e47935bd5e19eef980