add variables for which branch to fetch for external extensions, changed order of tasks since source task cleans the directory and removes the artifacts from the previous tasks.
add variables for which branch to fetch for external extensions, changed order of tasks since source task cleans the directory and removes the artifacts from the previous tasks.

valadas/Dnn.Platform,robsiera/Dnn.Platform,bdukes/Dnn.Platform,wael101/Dnn.Platform,mitchelsellers/Dnn.Platform,RichardHowells/Dnn.Platform,nvisionative/Dnn.Platform,svdv71/Dnn.Platform,RichardHowells/Dnn.Platform,wael101/Dnn.Platform,RichardHowells/Dnn.Platform,robsiera/Dnn.Platform,mitchelsellers/Dnn.Platform,bdukes/Dnn.Platform,nvisionative/Dnn.Platform,RichardHowells/Dnn.Platform,bdukes/Dnn.Platform,bdukes/Dnn.Platform,svdv71/Dnn.Platform,robsiera/Dnn.Platform,wael101/Dnn.Platform,dnnsoftware/Dnn.Platform,nvisionative/Dnn.Platform,valadas/Dnn.Platform,svdv71/Dnn.Platform,EPTamminga/Dnn.Platform,mitchelsellers/Dnn.Platform,dnnsoftware/Dnn.Platform,EPTamminga/Dnn.Platform,valadas/Dnn.Platform,EPTamminga/Dnn.Platform,dnnsoftware/Dnn.Platform,mitchelsellers/Dnn.Platform,dnnsoftware/Dnn.Platform,mitchelsellers/Dnn.Platform,dnnsoftware/Dnn.Platform,valadas/Dnn.Platform,valadas/Dnn.Platform