Solved minor issues and unified criterion in node tutorials

Change-Id: Ifb512f007a2a692a8f374d3c944d07f9c033dc87
Merged and ordered "Contribute" and "Mastering" sections

Change-Id: I007cfd8ea92eefa4a2c412459c3cd24395d18498
Added script to fix 2nd level links in mastering section

Change-Id: Ie2e00a4a0c273443673f620f80505dd46d315ff2