add dynamic image creation code & json refactor

[aparcar]

again, make JSON files more like upstream:

• images: use dict instead of simple file. This allows adding information like checksums or types. Again, I dealt so much with heuristics withn OpenWrt build system that I avoid it as much as possible. From my side I'd remove fragments like findCommonPrefix and just rely on upstream info.
• commit: replace with version_commit (as there is also version_number
• link: replace with url as link referes to something clickable in the browser while url is more generic, including machine reads
• activate sort_keys in collect.py, this creates reproducible json files and surely makes some JSON parser happy
• %foobar: instead of using % I changed the replacement to mustache0 which is also usable via Pythons format() function and easier to read. Say a string like %target-info/foobar could mean a variable target or target-info, using {target}-info/foobar makes things easier
• %file: remove this entirely and just append whatever desired file at the end. Is there any case where the downloaded file is not at the end?

all these changes where done to be compatile with the asu, meaning a image builder backend that creates images with specificed packages on demand. Example code is added within the top of index.js. The server takes version, profile and packages as arguments and returns within a few seconds a freshly build firmware, which is automatically shown in the frontend.

Signed-off-by: Paul Spooren mail@aparcar.org

[mwarning]

@aparcar Let's keep findCommonPrefix. It saves some spaces in the JSON and is a very reliable approach. I do not think the upstream JSON by openwrt will be able to (and probably shouldn't) satisfy the specific needs of the selector. But it can surely help, but not replace.