Until now, if a tarball couldn't be downloaded from its own URL, the
pipeline would completely stop. This is very annoying because as the number
of software increases, the possibility of atleast one of the software
tarball URLs being in-accessible (for example because maintainance)
increases. Some webpages may also have problems in some locations.

With this commit, a `mirror.conf' file has been added to the
template. Through this file, a project's designer can define a different
mirror to use for their project. When a software tarball can't be
downloaded from its original URL, the template will parse the
`mirrors.conf' file and look for the software in those servers.

To do this, it is necessary that when possible, the tarball names on the
mirrors be the same as the tarball name in the software webpage. Cases when
its not possible is when the tarball name doesn't actually have the
software name in it.

But it is necessary to check this a little more. Until the tests are done,
I'll keep this on a separate branch.