Improve handling of non web3 enabled browsers

[guillaumegaluz]

I was on Safari and filled in the whole form for adding a new project. Clicked "Add Project" and nothing happened. Checked the JS console:

Error adding a project: 
Error: Network error: Please use web3 enabled browser

I think it would be nice to let the user know earlier in the "Add Project" flow.
Maybe check if window.web3 === undefined and if so, add a banner at the top of the form to alert users they should switch browser now?

I'd love to make a PR, just want to raise this first and see if you think it's worth fixing (and if yes how)