Preserve commit message when switching to the History tab (jupyterlab…

…#931) (jupyterlab#836) (jupyterlab#971)

* Move commit message state to git panel (jupyterlab#931)

* Preserve commit message when commit fails (jupyterlab#836)

* Fix unit tests from refactor (jupyterlab#931) (jupyterlab#836)

* Rename commit message state variables (jupyterlab#931)

* summary -> commitSummary
* description -> commitDescription

* Preserve commit message when refusing to set identity when committing (jupyterlab#836)

- Raise error instead of returning false on fail setting identity

* Refactor commit and commit message handler functions

* GitPanel.commitFiles now handles all commit actions
* Refactor GitPanel spec to test commitFiles function instead of commitStaged
* Change commit message handler functions to be more generic

Bump to version 0.31.0-alpha.0

Bump to 0.30.1

Use latest nbdime (jupyterlab#926)

nbdime styles are not imported (jupyterlab#919)

* Import some styles from nbdime-jupyterlab

* Import additional styles from nbdime

* Move import to base

* Correct comment position

Merge pull request jupyterlab#918 from meeseeksmachine/auto-backport-…

…of-pr-917-on-jlab-2

Backport PR jupyterlab#917 on branch jlab-2 (Change commitAndPush default to false)

Merge pull request jupyterlab#875 from jupyterlab/fcollonval-patch-1

Bump to beta.2

Add jupyter_packaging for publication

Remove version matching

Version are aligned by code design

Bump to v0.23.3 (jupyterlab#850)