Add support for using Jsonnet library on the jpath

[parano]

Nice work! Have been looking for a plugin like this on Intellij.

I noticed that currently import statement only works for a relative path. Would love to see support on the 'jpath' option, which specifies additional search paths for jsonnet library.

The vscode jsonnet plugin supports this via the "libPaths" variable in settings:
https://github.com/heptio/vscode-jsonnet/blob/master/compiler/editor/workspace.ts#L75