Increase the size of the addresses in protobuf.
Fix layout2.c to handle longer addresses.
Add a field bech32_prefix to coins.h
Adapted the coins-gen script.
Added bech32 support in signing.c and transaction.c
Having CoinType using the protobuf structures has several disadvantages.
- We always need to change trezor-common if we need a new field (like
bech32 prefix)
- Every time Trezor initializes it sends all this information out and
nobody cares.
- The protobuf structures add storage overhead due to their fixed size.
I also removed most of the `has_` fields except for forkid:
- `has_segwit` was merged with segwit
- `has_coin_shortcut` can be replaced by test for NULL if necessary.
The fields were reordered for better padding.
