Add button to trigger sync in sync logs page

[flodolo]

Fixes #3557

[mathjazz]

Nice work!

Left a few suggestions. Before we merge, I might want to make a small CSS change to account for adding the ability to disable sync in the future.

[flodolo]

Follow-up from earlier conversation: these are all the page using table-sort

pontoon/localizations/templates/localizations/widgets/resource_list.html
pontoon/projects/templates/projects/widgets/project_list.html
pontoon/sync/templates/sync/log_errors.html
pontoon/sync/templates/sync/log_list.html
pontoon/sync/templates/sync/log_project.html
pontoon/tags/templates/tags/widgets/tag_list.html
pontoon/teams/templates/teams/widgets/team_list.html

They all seem to already include table.css, so it would make sense to move all table-sort rules there. Happy to leave this to you ;-)

[mathjazz]

Made a couple of minor changes. When and if we make more changes to the sync log, we'll adapt again if needed.

@flodolo Could you please take a look at the changes and test on stage?

[flodolo]

Changes look good (both stage and local instance) 👍🏼