Add Symlinks in the path for several packages + Permissions fix

This pull request adds symlinks into /usr/local/bin as a post installation step for the following packages:
- git
- node
- ruby
- python

Additionally, it also fixes the permissions and the ownership for the installed files. 
Before the fix the files were assigned to the same uid of the user building the package on the build system which could be a problem since a user on the synology might have had the same uid and thus might have been able to tamper with the installed files. Now all the files are owned by root.

Other packages might be affected by the same problem.