Allow users to customize displayed columns

[MisterPhilip]

Also related to #80, it'd be nice to allow users to customize what columns are shown on the devtools panel. 9b0a5f3ac51feafbfddfa454f6924e8dd16c0ab5 started the process of this where you could add it in via settings, but I'd like to expand it more to include the context menu.

However, we need to decide if the match should be done on the raw parameter key (e.g. pt), or the friendly name (e.g. Page Title). Allowing it on the raw parameter key would be easier long term for us to keep maintained, but since parameters differ between providers it might be confusing to users why one provider has a value when another does not. The friendly name would likely make more sense to end users, but could become a logistical nightmare of keeping things updated. We also need to consider parameters that are renamed by the user; do we use those or Omnibug's provided name?

I feel like it'd be best to do a combination of the two: show the friendly name, but only match for that one provider based on the raw parameter key.

We'll run into a similar issue when we update exporting (#120) to show all fields and not just the raw values.