Allow customizing UI text

[jnunemaker]

Each gates text/help/instructions should be customizable so companies/developers can make it feel more like there own. I can also see providing an actor to instance conversion block for changing things like User:6 to @jnunemaker or whatever makes sense.

[721p]

We use rails global ids as the flipper_id value which could make this pretty trivial to implement

[AlexWheeler]

@jnunemaker what are your thoughts on doing this via the configure block? similar to how the adapter can be set via Flipper.configure.

We could have a Flipper::UI.configure. The downside is anyone couldn't customize since it would need to be set in the initializer, but it could work well.

[jnunemaker]

@AlexWheeler I like that for anything that needs to be customized. 👍

[jnunemaker]

This is done. UI text can now be configured.