perf: reduce coolwsd memory footprint

[mmeeks]

coolwsd currently stores all of the files we serve in-memory to avoid needing to touch the file-system after start.

Arguably this is good for security, however in some circumstances eg. the appimage use case that's not going to improve things much, at quite some cost in memory.

We should not store un-compressed files in-memory, but only the zipped ones; we should de-compress from these (which is super-fast) if/as/when needed to serve them (in one-shot - that should be a very unusual code-path). That should save around ~40Mb of memory for coolwsd: not earth shattering, but worthwhile - and ~8% of coolwsd's memory usage.

[mmeeks]

@Ashod might be interesting for you =)