Add ability to drag/toggle columns

[bugzilla-to-github]

This issue was created automatically by a script.

Bug 1586822

Bug Reporter: @mathjazz CC: @VishalCR7

As part of Translate.Next we dropped the ability to resize columns, since the functionality would change due to bug 1586820. Once that bug is fixed, we should re-implement it and possibly add the ability to toggle the string list completely.

Taken from #2081: It would be nice if Pontoon remembers the panels width, stores somewhere in the browser, so it survives reloading the page or even closing and opening tab/browser again. IMO it does not have to be stored server side, as the desired width may vary for different devices.

[bugzilla-to-github]

Comment Author: @mathjazz

Inspiration from the [email protected] branch: https://github.com/mathjazz/pontoon/commit/8652f0961b51d944634c0552cecd6362ed315309 https://github.com/mathjazz/pontoon/commit/4e3026447be0366618a131d4133ef596a1976343

[mathjazz]

Relatedly, one should also be able to resize/toggle Terms/Comments panel on behalf of the Machinery/Locales panel: https://discourse.mozilla.org/t/req-right-side-pane-machinery-locales-draggable-to-resize/85168