Minimize tx sending progress

[jacogr]

As soon as the transaction gets into waiting for tx state, the dialogs (transfer, contract deploy, contract execution, etc.) the tx dialog should

• minimise to the bottom right
• multiples can be stacked
• keep track of confirmation count
• disappear when x (6/10) confirmations received

Basically it should allow the user to get on with his/her job while still allowing them to keep an eye on the transactions busy.

[ngotchac]

NB : could be nice to have them semi-persistent (ie. in local storage), especially for contract deployments : be able to close the UI when the contract is being deployed (eg. with a min block param) and still have it added to the contracts view when it's deployed

[ngotchac]

Closed via #4942