Rewrite Dev docs

[ct-martin]

Dev docs are no longer up to date, once #29 is done they should be rewritten.

[ct-martin]

Did some updating, still will be a WIP as build process is still being remade.

[ct-martin]

Sidebar and main development (subsection) page have been updated with new content, the old building docs have been moved to links on the new page and marked as legacy. Also removed the unneeded UNIX permissions guide from the wiki homepage as this can easily be looked up. I'm going to leave this issue open for now since this work isn't complete.

[ct-martin]

#100 was completed as part of this

[ct-martin]

Currently up to date with build procedures, will continue to update (inc. with @axk4545 & @CoffeeFrame changes for building)

[ct-martin]

Also, will be updated due to change of plans in #29 as part of ^

[Tjzabel]

@ct-martin @axk4545 Have the Development Dos been successfully rewritten?