Switch to gluon v2017.1.8

Updated Jenkinsfile to use gluon v2017.1.8 instead of v2017.1.7.

Provide Jenkinsfile to build firmware with jenkins

A few parameters lacked descriptions. These were added. Architectures do
not have a description yet.

As the current release does generate any artefacts to output/modules,
this folder will not be stashed or archived

As with the current release sunxi seems not to be supported, this
architecture will not be build by default

In order to build our firmware with jenkins, we need a jenkins pipeline
script. With this commit, this script is provided. Documentation can be
found within the Jenkinsfile.

missing commas, other minor changes

"Welcome *to*" and only single blank

Option to override build date

Setting BUILD_DATE overrides the date used in the generated image names.
With this it is possible to have a consistent build date across all
architectures, making it easier to identify a release. Furthre more it
might be the key to have reproducible builds

Feature/2017.1.x

Merge branch 'feature/2017.1.x' of https://github.com/freifunk-stuttgart/site-ffs into feature/2017.1.x

gluon-web-mesh-vpn-fastd allows the user to switch between the security and performance VPN settions.

Feature/remove vpn schluessel ml hinweis

remove ibss