Ability to skip suites

This feature allows to skip any suite completely,
for particular browser or particular version of
a browser.
Show skipped test in tree reporter
Show skipped tests in html reporter
Show skipped tests in teamcity reporter
Document `skip()` method
Add info about skip method to changelog
Merge suite.skip support

This feature allows to skip any suite completely,
for particular browser or particular version of
a browser.
WIP: find function
captureElements replaces static/dynamic elements

setElements and setDynamicElements was used to specify both
active elements and elements to take screenshot of. Now, when
`find` is used for active elements, they should be removed.

`setCaptureElements` accepts a list of selectors. If element was
not found, it will be ignored (same was as it was for dynamic
elements).
WIP: before hook