Do not pass kMobileFlags for all TIZEN builds using ubrowser

Do not pass kMobileFlags for all TIZEN builds using ubrowser

kMobileFlags are defined in ubrowser/main.cc and are passed to chromium in case
ubrowser is launching with mobile param.

However, as |!desktop_ui| is also true for all TIZEN builds those flags are
unexpectedly set for them. As for OS_TIZEN_MOBILE they are just duplicated and
do not bring side effects whereas for OS_TIZEN_TV they are not expected.

This patch passes kMobileFlags in case "ubrowser --mobile" only.

Additionally, this patch gets rid of custom EFL command line
"use-mobile-viewport-style" as it can not be propagated to Renderer by default.
For OS_TIZEN_MOBILE |UseMobileViewportStyle| is set by default on src/ side [1].

This patch introduces a new EFL command line:
"ewk-enable-mobile-features-for-desktop" in order to turn on a bunch of
settings for which there is no command line switches. This allows desktop
"ubrowser --mobile" to have similar set of features that mobile build has.
Secondly, we stop abusing |UseMobileViewportStyle| in |ApplyCustomSettings|.

[1] http://165.213.202.130/gerrit/#/c/97109/1

Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=14816
Bug: http://web.sec.samsung.net/bugzilla/show_bug.cgi?id=15031

Reviewed by: a1.gomes, sns.park

Change-Id: I7dd9f693f53abab0916e6113bbc15bfe635a3159
Signed-off-by: Grzegorz Czajkowski <g.czajkowski@samsung.com>