Move contribution process from designs.a.o to policies

We have a stub in guidelines for the contribution process. Move the
content over from designs.a.o and move to policies.

Add in alias for `old-designs` to record the location used on
designs.a.o that we can be used once we've dropped all the contents
of designs.a.o as a redirect to the website.

Flag file to be generated as PDF since it's a document from
designs.a.o.

Remove `guidelines` from the main page as it's now empty.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/_index.md

@@ -70,7 +70,6 @@ Apertis provides a number of pre-built images for Intel (64-bit) and ARM (32-bit
 * [Mailing lists](https://lists.apertis.org/)
 * [Architectural documentation]( {{< ref "/architecture" >}}) 
 * [Development guides]( {{< ref "/guides" >}} )
-* [Development guidelines]( {{< ref "guidelines" >}} )
 * [Concept designs]( {{< ref "concepts" >}} )
 * [Supported APIs](https://developer.apertis.org/latest/apis.html)
 * [App developer portal](https://developer.apertis.org)

content/guidelines/contribution_process.md

-+++
-date = "2019-10-25"
-weight = 100
-
-title = "Contribution Process"
-
-aliases = [
-    "/guidelines/howtoworkwithpatches.md",
-    "/old-wiki/Guidelines/HowToWorkWithPatches",
-    "/old-wiki/Guidelines/Contribution_process"
-]
-+++
-
-Please see the [contribution
-process](https://designs.apertis.org/latest/contribution-process.html)
-on <https://designs.apertis.org>.