CHE-3570. Add ability to turn on/off autosave mode for editor content

[RomanNikitenko]

Signed-off-by: Roman Nikitenko rnikitenko@codenvy.com

What does this PR do?

Add option 'Enable Autosave' to editor preferences.
Provide:

• sync opened file content with working copy on server side when the file has unsaved data.
• update editor content for 'Split' actions when Autosave mode is disabled.
• processing 'Reconcile' operations for java files and pom.xml files from working copy on server side

What issues does this PR fix or reference?

#3570

Changelog

Add ability to turn on/off autosave mode for editor content

[codenvy-ci]

Build # 2651 - FAILED

Please check console output at https://ci.codenvycorp.com/job/che-pullrequests-build/2651/ to view the results.

[codenvy-ci]

Build success. https://ci.codenvycorp.com/job/che-pullrequests-build/2666/

[davidwindell]

Is there a Ctrl + S save command when autosave is turned off?

[RomanNikitenko]

@davidwindell Yes, there is Ctrl+S hot key for save a content of current editor

[codenvy-ci]

Build success. https://ci.codenvycorp.com/job/che-pullrequests-build/2711/

[slemeur]

@vparfonov + @RomanNikitenko : This is a new capability and you need to request PMs to review the PR before merging. That PR actually needed documentation and release note information.