Start redesigning jetpack to be a passive upgrade that integrates with regular movement control.

The current in-progress version comes without any weaknesses or limits such as
fuel. Use g_debugMove 1 to debug.
Improve Jetpack controls.
Don't apply sprint modifier in air.
Make jetpack use a refilling fuel.
Make jetpack fuel display pretty.
Disable jetpack for a short time when hit by another client.
Merge branch 'gameplay/jetpack', remote-tracking branch 'remotes/origin/master' into gameplay/testing
Merge branch 'gameplay/ds' into gameplay/testing
Synchronize jetpack fuel calculation to get rid of prediction errors when out of fuel.
Possible overflow when loading models; overlap with fake model handles.

This adds MAX_SUBMODELS, initially set to 512. This avoids breaking netcode
compat.

The fake handles for box and capsule are adjusted so as to be outside the
submodel handle range.

Closes: #268, #269, #270

Ref. https://github.com/zturtleman/spearmint/commit/d1c612ee3623a6b25050f0c913a713184f7cf859
Remove an obsolete config file.
Fix visibility of jetpack effects on other players.
Merge branch 'gameplay/jetpack' into gameplay/testing
Don't error out when asked to render weapon icon WP_NONE.
Simple colouring of the predicted RGS % efficiency.
Merge branch 'master' into gameplay/ds