New GUI binary name: pilot

[yungyuc]

For a long time we are using a non-distinguishable name "viewer" for the GUI binary for modmesh. There is an issue to discuss the new name: #400 .

I plan to rename it to "pilot". The sub-module modmesh.view will become the sub-package modmesh.pilot. All GUI code should be collected under modmesh.pilot. No GUI (Qt) code should be outside it.

[tigercosmos]

Why do you choose "pilot"?