feature: redirect login from an app page back to that app page after login

[nick1udwig]

See #425. PR #428 fixes the bug by redirecting from app login to node login, but user must then navigate back to app endpoint. A better behavior would be to, after login, redirect back to app endpoint.

[gtimoth]

@nick1udwig request to also do this for URL params. Note that URL params are currently lost in two scenarios:

1. when logging in
2. when redirected to secure subdomain, e.g. baseorigin.com/app:pkg:dev.os/?param=foo -> pkg-dev-os.baseorigin.com/app:pkg:dev.os

This is an important feature for dartfrog.

[nick1udwig]

#439 merged