Fixed the Taable and SplitTable classes

* Changed the XPATH expression and made the search for elements start from a
root element instead of from DOM root
* Renamed occurances of browser to sel in the tasks.py page
* Removed the is_displayed() method and replace occurances with
sel.is_displayed()
Small docs fix
Add helper func sel.value() - to ease access to text in input/select elements
Add flash.assert_message_contain() to be able to check only parts of flash messages
Merge pull request #590 from psav/fix-table

WIP:Fixed the badness
Add server name test
Merge pull request #593 from psav/fix-docs

Small docs fix
Merge pull request #595 from jkrocil/flash-contain

Add flash.assert_message_contain()
Merge pull request #594 from jkrocil/sel-value

Add helper func sel.value()
Merge pull request #596 from jkrocil/test-server-name

Add server name test