Add option to disable the accumulation of tk-apps in a global atom

[vemv]

Use Case

In a dev environment (but certainly not in production), the register-sighup-handler defn is largely unnecessary. Because of that, the global tk-apps atom also becomes unnecesary, particularly if one has a different means of accessing a global app object (which is very usual under a Reloaded workflow).

By accumulating apps in this atom, one creates hard memory references that can plausibly create a memory leak.

Describe the Solution You Would Like

Inrtroduce a java system property which elides this call:

trapperkeeper/src/puppetlabs/trapperkeeper/core.clj

Line 158 in c943510

(swap! internal/tk-apps conj app)

Said property would typically enabled only in dev envs.

Describe Alternatives You've Considered

One could keep the functionality but changing it to use WeakReferences instead. Seems a needless source of complexity though.