Memofields intent does not handle ICA owned validators

[joe-bowman]

Summary of Bug

The parsing of the intent field expects 20 byte valAddr, but this can be 32-bytes in the event of a ICA controlled validator.

[joe-bowman]

Supporting this means we have to length prefix the validator string.

Currently we can support:

Memo size: 256
After base64 overhead: 192
Minus prefix and field length: 190
190/21 (weight + addrbytes) = 9.04

With address length prefix, 190/22 = 8 vals (no change)
All 32 byte val addresses -> 5 vals (unlikely)

It makes the number of validators that can be selected dependent on which validators are selected, so needs to be considered alongside front end changes.

[joe-bowman]

Note, this will require corresponding front end changes and must not be merged until the front end is updated ready to support on release.