Mesh shields (#2013)

# Description
This PR is based on the request raised in #2013 and uses the shield mesh supplied by @lionhearted adapted for the Wave as the Lanner has been removed.

This simply fades a mesh based shield in/out based on what percentage of it is left so it's a direct replacement for the existing effect. I'm too wiped out to do hit effects and things at the moment.

# Issues
There's some funky code I'm not happy with in Shield::Render where it acquires the shield material and sets the specialParameter0 so it can pass the shieldStrength through.

Also the idea of it being in with the other meshes feels a bit hacky so alternative suggestions are welcome.

# Addtional work required
Only the Wave has a mesh shield at the moment and since this disables the older way of doing shields it means none of the other ships have them. So we need people to create shield meshes for all of the ships.

Thanks,

Andy