Login capabilities

[guy881]

Server:

• flask session authentication, user is required to store secret key (as environmental variable called MULTIVISOR_SECRET_KEY),
• /api/login, /api/logout and /api/auth endpoints,
• username and password stored in multivisor configuration file,
• login_required decorator for restricting the access to the view,
• constant time password comparison,

Frontend:

• Login page
• Add menu with logout button
• Show menu and toolbar links only if user is authenticated
• Redirect to login page if user is not authenticated
• Redirect to homepage if user is already authenticated and goes to login page

I believe the target should be a future release branch but I can only choose master. Let me know if I should squash commits or something.

Issue: https://github.com/tiagocoutinho/multivisor/issues/8

[tiagocoutinho]

@guy881, LGTM.

I have created a develop branch. Could you change this PR target branch to develop? Thanks a lot for your contribution.

[guy881]

Ok, @tiagocoutinho, done!

[tiagocoutinho]

@guy881, there seen be conflicts so I cannot merge. Could you have a look? thanks

[guy881]

@tiagocoutinho are you sure about this? Maybe I am doing something wrong, but github shows no conflicts to me.

[tiagocoutinho]

Strange... I have this:

[tiagocoutinho]

Ok, doing it by hand...