Add ability to tab through unapproved txs

[whymarrh]

When a long list of unapproved transactions have built up, there should be some way to tab through all of them.

[bdresser]

@whymarrh I think it'd make sense to have a visual indicator as well for non-pro uses. Check out #3425, where we're adding a small "1 of 3" indicator.

If we let the user flip through the transactions themselves, won't we increase the likelihood of nonce issues? Say, if the user tries to approve the third tx before the first?

[whymarrh]

If we let the user flip through the transactions themselves, won't we increase the likelihood of nonce issues? Say, if the user tries to approve the third tx before the first?

The nonce for a new transaction is calculated when the user confirms it so we shouldn't have issues from what I understand.

[whymarrh]

I'll un-assign myself from this for now until the work started in #3425 is complete

[bdresser]

design issue at MetaMask/Design#30

[tmashuang]

Closing due to inactivity, all other related issues seem to be closed. Multiple transactions and batch transactions have been implemented.