Long press on empty fields should show context menu if needed

Long press on empty fields should show context menu if needed

If one long-presses an empty input field, we enter selection mode:
magnifier is show, etc.
This is a bad UX, and does not match other mobile browsers.

Patch changes that to show context menu right way, with clipboard
options if applicable. This matches other mobile browsers: firefox
mobile, chrome and s-browser.

Bug: http://107.108.218.239/bugzilla/show_bug.cgi?id=14910

Change-Id: I002f57a1224431a915740d87e7694db358153493
Signed-off-by: Antonio Gomes <a1.gomes@samsung.com>