hotswap is missing from the norns/lib

[jaseknighter]

fix for https://github.com/monome/norns/issues/1761

solution: copy hotswap.lua file from the crow lua lib to the norns lua lib

testing: after copying the code and restarting my norns, i tested from the maiden repl using the code from the crow hotswap documentation:

sequins = require('sequins')
hotswap = require('hotswap')
-- the sequins is overwritten, but the playhead is preserved
hotswap.seq = sequins{1,2,3}
hotswap.seq() --> 1
hotswap.seq() --> 2
hotswap.seq = sequins{4,5,6,7}
hotswap.seq() --> 6