Add wait where needed in selenium and webdriver tests since they run faster

Since we upgraded to selenium 2.39.0 and FF26, functional test execution seems to be faster.

As a result, we might see some new heisenbug appearing because some waits are now required.

We did not see it before because tests were running slower.

For instance https://qa.nuxeo.org/jenkins/job/FT-nuxeo-master-webdriver-dam-tomcat_permanentCheck/3480/ (See https://qa.nuxeo.org/jenkins/job/FT-nuxeo-master-webdriver-dam-tomcat_permanentCheck/3480/artifact/nuxeo/nuxeo-distribution/nuxeo-marketplace-dam/ftest/webdriver/target/screenshot-lastpage-com.nuxeo.functionaltests.ITAssetPageTest-navigateToDM6264083921522959136.png).

It seems we don't wait after clicking..