Redirect after checkout, other improvements

[mds1]

Changes:

• After checkout, redirect to /grants page and show success alert (#22)
• Refactor cart header layout to match figma mockup
• Filter out transactions that have zero balance (#47)
• Check that user has sufficient ETH/token balance before sending donation tx (#46)
• Clear cart contents after checkout (use the cart class) (#56): This is done before the redirect to ensure the cart is cleared, because a user may see the tx submitted and close their window before the redirect. However, it results in a bit of an awkward UX as the cart is empty while the redirect is in process. I'm open to suggestions here
• Bot on checkout page moves when updating amount (#60)
• Restrict input field values (#63): In the interest of time, for now this is just simple validation using the input min/max parameters, so only affects when using arrow keys, not when typing

[mds1]

@apbendi This is ready to rebase and merge if you want to review it. Only thing left would be kudos support (#55) but I think @owocki will do that in a separate branch

[apbendi]

hey @mds1, this is a nitpick, but do you think you could squash a lot of those WIP commits. Looks like maybe all of these could just be one atomic commit for getting POSTs working?

@mds1 WIP: Begin configuring checkout POST requests 2acfa08 @mds1 WIP: Add post requests (currently failing) 1e07058 @mds1 Fix POST request: switch body to x-www-form-urlencoded f5932e3 @mds1 Add csrfmiddlewaretoken a0b3f93 @mds1 saveSubscription POST request now succeeds 0e1f6c8 @mds1 saveSplitTx POST request now succeeds 84d6c3f

[mds1]

Wrong target branch (is master, should be bulk-grants), so closing this PR

[mds1]

New PR: #64