Merge develop into master

TO BE TESTED

Deployed on https://codabench-test.lri.fr/

Cleanup and quota

• #918
• #958

At the bottom of the resources interface:

• Delete unused tasks
• Delete unused datasets
• Delete unused submissinos
• Delete failed submissions

Phase status fixed

• #934

• Make a submission in a never ending phase

• Play around with phase dates and make submissions

Dynamic news edition

• #952

• Add announcement and news

• Remove announcement and news

• Add documentation (in "administrator procedures"?) about this feature, with screenshots

https://github.com/codalab/codabench/wiki/Administrator-procedures

Number of entries in leaderboard fixed

• #966

• add a submission to multi-tasked phase. without this fix it will show number of submissions x tasks in the leaderboard

Leaked users fixed

• #929

Organization

• #976

• In the submission interface, the "Submit as..." scrolling bar should propose to create an organization if you don't have any.

• #959

• Try to add and delete an organization

Add phase fixed

• #963

• Add a phase using the editor

• Try different dates, never ending, etc.

• Make a submission to the new phase

• Remove some phases

Update text in front page

• #983

The paragraphs "What is CodaLab", "What is Codabench", "History of CodaLab", etc. was updated.

• Proof-read the paragraphs
• Test the links