Fix cite completion concatenation

Fix local reference completion lookup

Fix `view` argument being overwritten by local reference lookup
in open documents.

Use built-in "oem" encoding for decoding shell output

As of python 3.6 `"oem"` encoding is supported to represent
codepages used in Windows' terminals.

Read bibfiles using context manager

Refactor command/environment completions

Refactor command and environment completions, both of which using
latex_cwl_completions module as backend for completions from cwl files.

- properly implements environment-name auto-completions via EnvFillAllHelper
  -> LatexCmdCompletions no longer has to deal with them

- replaces `latex_own_command_completions` module, which was a mix of command
  and environment-name completions before.

- add ST4 kind information for richer user experience

- remove hacks to asynchronously load cwl files in a background threaded
  as whole completion query is already outsourced to ST's worker thread.

- overall simplification of CWL file loading

Fix failing list and tuple concatenation

Add kind icons to BibTex completions

Use common global settings function

Fix _InputQuickpanelListener name

ST4 ignores all protected module attributes (prepended with underscore).

Fix _InputQuickpanelListener name

ST4 ignores all protected module attributes (prepended with underscore).