[M34 Merge] Fix for the 'Reload' button not displayed on page load finish

[M34 Merge] Fix for the 'Reload' button not displayed on page load finish

[Cause] "load,started" callback was triggered more than once,
e.g when an iframe present on the page was reloaded. In a browser,
it caused the status bar to be refreshed and reload button to
be changed into cancel button. Additionally, in such case, the "load,finished"
callback was not triggered and the cancel button never changed back into
reload.

[Solution] "load,started" and "load,finished" should be called
only once, when a page is loaded.

M34-merge: http://165.213.202.130:8080/#/c/69958/
Bug: http://168.219.209.56/jira/browse/TNEF-172
Reviewed by: Antonio Gomes, Piotr Grad, SeungSeop Park

Change-Id: I4b47a3833cbf487e2473c2fe70d2340111b5c807
Signed-off-by: Lukasz Krok <l.krok@samsung.com>