Language Server Protocol support

[fabawi]

LSP auto-completion for citing as you write is working (currently experimental). Local Bibs are now shown in LSP panel, however minor issues still exist, including:

• Writing to linked documents is not implemented. Only writes to the corresponding bib file from the LSP provider
• Handling updates from LSP provider to existing local bib content is not yet possible. Currently, it only adds new entries
• [Optional] Update the LSP provider's content based on local bib file changes