add panoramio layer and button to toggle visibility of that layer

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/pm_tour/trunk@75628 735d13b6-9817-0410-8766-e36946ffe9aa
make usage of panoramio configurable via constants

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/pm_tour/trunk@75636 735d13b6-9817-0410-8766-e36946ffe9aa