Storing the history of reload tasks in a user session

[ziollek]

Description

Some client requests that affect varnishes configuration trigger reloading tasks that are applying changes on varnishes.
If the task fails modal window is displayed with detailed information on what was going wrong.
Unfortunately after closing that window, the user is not able to check again what has happened.
Some client requests that affect varnishes configuration trigger reloading tasks that are applying changes on varnishes.
If the task fails modal window is displayed with detailed information on what was going wrong.
Unfortunately after closing that window, the user is not able to check again what has happened.

Expectations

Reloading tasks are stored in a user session. There is a view with the list of the last (size of the list is configured in settings) reloading tasks generated by a logged user.
User has the ability to preview details of each task such as:

• what set of clusters was affected
• what was the status of the task on each cluster
• detailed error if occurred

This issue requires changes described in #415