delay grid interface: add performative controls

[dndrks]

current behavior: the delay grid interface has a 4x4 square with a bank selector which is subject to the main performance page's arp rules, but there are no additional controls

proposed behavior: add the following performance controls to the delay grid page:

• [x] alt + pad = remove from arp
• [x] arp enable/hold button
• [x] loop button
• [x] zilchmo 4

[dndrks]

added arp controls with #17