Install & Usage Improvements: Add single installation script and java-language-server entrypoint script

[jaybocc2]

I ran into some issues w/ the existing installation scripts on mac so i thought i'd share my fixes and i also took the time to add a unified installation script and a standardized runtime script so that there is minimal configuration between OS'es if you switch frequently between linux / mac / etc.

I don't use windows so not sure how much of this will work there.