pgAdmin 4 commit: Add controls and shortcuts forcommenting/uncommentin

Add controls and shortcuts for commenting/uncommenting code in the SQL Editor. Fixes #2456.

Take the opportunity to tidy up the menus and add access keys to appropriate buttons.

Branch
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master

Details
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https://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=1e1a9f2cf4a76a4761bad780317b0908a565ee00

Modified Files
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docs/en_US/keyboard_shortcuts.rst                  |   6 +
web/pgadmin/static/bundle/codemirror.js            |   1 +
.../tools/datagrid/templates/datagrid/index.html   |  65 ++++++---
.../sqleditor/templates/sqleditor/js/sqleditor.js  | 152 ++++++++++++++++++++-
4 files changed, 204 insertions(+), 20 deletions(-)