Enable showing image title/hover text on long press

Listens for long click in webview, if it is on an image, gets its url, looks for the title tag before or after the url and shows an alert dialog if found.

Searches for title text before/after the image url using two separate patterns, since I couldn't figure out how to handle if a group regex match (in parentheses in the pattern string) is equal to null or not.

Conflicts:
	app/src/main/java/fr/ydelouis/selfoss/fragment/ArticleFragment.java