Revamp the tipping system to include a BAT amount slider

Revamp the system to include a slider, with values being multiples of 0.5 BAT. The value of BAT has increased a lot in recent times. It is illiogical to give options for only 1 and 5 BAT and nothing in between, which is pretty counterintuitive… I had to tip 1 BAT multiple times to give a value in between. 5 BAT may be too high a value for people to part with, and 1 BAT may not be enough to satisfy people’s generosity. Brave should give more granular control over how much we want to tip.