Add a way to jump to top/bottom of ledger file

It would be useful to add a way to quickly jump to the bottom or top of the ledger file. Currently it can be quite annoying to check if a new transaction has been added, if you have to scroll down a few thousand lines.

A similar app , beancount-mobile (https://github.com/xuhcc/beancount-mobile), simply uses two buttons of an upward/downward pointing arrow to allow this.

Start by locating the ledger file view and its existing scrolling or navigation controls. Add clearly identifiable controls for jumping to the top and bottom, then verify that each reaches the corresponding end of a long ledger file.

Written by the indexing model from the issue text.