Allow setting file URLs with eg. .url.txt files

[NikkyAI]

i am going to try to describe the feature the way SKLauncher uses it because i think its very powerful and useful to have

given a file eg: mods/someMod.jar it would usually redistribute that jar
unless there exists a file mods/someMod.jar.url.txt with a single line inside specifying the url

this can be used to download from cursecdn, jenkins or wherever else the mod dev serves the files

It would be preferable to rehosting
and i would appreciate adding this, i need it for adding simple MCUpdater-fastcraft support to my modpack building stuff

[NikkyAI]

discussion on discord resulted in:

it should be possible to set via marker files
it should be possible to set in a single file where each line matches a file

additionally it would be nice if the same thing could be done for sided info:
<Module ... side="BOTH"> is currently on every entry