Improve debug logs

This allows enabling debug logs per a compilation unit or via
compilation time defines.
Add random(min, max) function for TestObject
Call showFullscreen from TestObject
Add timeout argument for TestObject::waitSignals
[sailfish-browser] Change "Filter" to "Search" in about:config

"Search" is now a generic placeholder ("sailfish_browser-ph-search") that
can be used elsewhere in browser as well.
Merge pull request #213 from rainemak/updateTranslation

[sailfish-browser] Change "Filter" to "Search" in about:config
Merge pull request #207 from rainemak/debugLogImprovement

Improve debug logs
Merge pull request #208 from rainemak/testObjectFixes

Test object fixes
Update tabId when contentItem changes