After installing a plugin, directly show the Plugins listing instead of an intermediate page

[mattab]

Current behavior

Currently when installing a new plugin, user is redirected to an almost empty page:

• When plugin is already activated:

• When plugin was not yet activated:

Proposed changes:

• Remove "Unzipping plugin" sentence
• Show the text "You have successfully installed ..." at the top of the Plugins listing, in a green success notification box
• When applicable, show the "Activate plugin" button (or change it to a link?) in the green notification

Advantages:

• one less page / click to go through
• the link "Back to marketplace" is not always correct, since after https://github.com/piwik/piwik/pull/11630 we can install plugins from the Plugins page directly, and therefore the "Back to Marketplace" won't bring back user to the right page
• Consistent with the rest of Piwik (when an entity is added, we always show a green notification)

[tsteur]

one less page / click to go through

That's not necessarily an advantage

I think this flow makes usability rather worse. 1.) Most users don't know difference between installing / activating a plugin and when you see it is installed most will think they are done. Many people also don't read so by showing a green notification and roughly seeing eg installed may be confusing. I would be very careful with using green color here and how the wording starts and ends if you go for a notification. 2.) The activate button may not be visible enough or not get so much attention that users actually realize there is another step to do in order to actually install the plugin and get it to work.

Sometimes having an extra page letting the user focus just on this is better than trying to remove a page. Maybe it could be instead done in a dialog or so where user can focus on that decision whether to activate plugin or not, or everything would be done via ajax in the same dialog etc.