Add modal element for Tip button with Web3 transfer

[marsskop]

• add Bulma's modal element that show on clicking "Tip" (https://bulma.io/documentation/components/modal/#javascript-implementation-example)
• this modal element has:
• • user and waiter confirmation (names, addresses)
• • amount of RUB to tip
• • "Tip" button
• call transferFrom on click and save the transaction to database

[marsskop]

on the "transferFrom" call here's a question: how to approve for the spender? or just use transfer?