Enable targets with the same name in multiple registries

[LachlanMarnham]

In cases where multiple registries have targets with the same name, the following resolution strategy should apply:

• If the target is found in only one registry, use it without further prompt.
• If the target is found in registry namespace 'default', and a target with the same name is found in another namespace, use 'default' without further prompt.
• If target is found in multiple non-'default' registry namespaces, prompt with the options

$ begin install
The target `install` was found in multiple registries. Please select one to continue:
[1] default
[2] global