add RuntimeInfo equals and hashCode
add RuntimeInfo.isValid method
remove warnings
add @NonNull annotations for getBuildBackend(IProject)
mode @NonNulls
fix warnings
fix synchronization in BackendManager
@NonNull (+1 squashed commits)

Squashed commits:

[ff3802d] fix warning
remove useless code
let RpcSiteFactory use ErlProject as parameter
use ErlProject as parameter for BackendManager
small cleanups
rename BackendProvider