Boost modal UI enhancements

• make the description of sidebar boosts more descriptive
• button should have the same shape as other buttons
• figure out why there is just one boost option and if there's always going to be just one, the UI should reflect that
• fix unexpected cursor pointer behavior
• if 'offchain' is default, it should be first
• move 'buy tokens' somewhere else or make it look different from the onchain/offchain choice