Provide more actionable data on the Activity page

Description

The current Activity page looks like a dump of data taken from the database.

We should repackage it to make it more useful, and to provide more meaningful, actionable data to the user.

Proposed solution

• Change names of "Push events" and "Merge events" to make them more user friendly
• Better layout for the Team tab
• Push events:
  • Show the latest pushes I've made on the last day/7 days/all time
  • Show the branches with the most push activity in the last day/7 days
  • Show the most active user who has pushed in the last day/7 days
  • Show the latest pushes (as we currently do)
• Merge events:
  • Show the latest merges I've made on the last day/7 days/all time
  • Show the branches with the most merge activity in the last day/7 days
  • Show how many branches have been merged to master in the last day/7 days
  • Show the latest merges (as we currently do)
• Comments:
  • Show the latest comments I've made on the last day/7 days/all time
  • Show the issues I've commented the most on the last day/7 days/all time
  • Show the MRs I've commented the most on the last day/7 days/all time
  • Show the latest comments made on the project (as we currently do)
  • Provide data about issues and MRs with the most comments in the last day/7 days
  • Provide data about the most active commenter in the project in the last day/7 days
• Labels: A new tab that would list
  • First we need to choose a label
  • the latest issues created or updated with this label
  • the latest MR created, updated or merged with this label
  • statistics about issues and MR with this label

cc @gl-product