Adding BAT token by default to accounts, component patching work

[ryanml]

Fixes: brave/brave-browser#4773
Fixes: brave/brave-browser#4924

This PR contains the initial patching strategy for overriding MM components without any actual patches :)

This adds BAT to the user list of tokens by default after creating their account

Ideally this would have been done just by placing the BAT token object in the default store, but this proved to be a little too complicated for a few reasons. A one time add via an existing action proved to be much more simple and reliable:

Main View:

Non Removable:

With other assets:

[ryanml]

@bbondy updated to use brave components,

[ryanml]

Unfortunately the way TokenMenuDropdown was set up didn't really make it prime for simple extension, so this is more or less the same file. No copy involved still

[bbondy]

I guess it's ok for us to fork certain components like this but we should try to avoid when possible.

[ryanml]

@bbondy this is ready for another look - this approach should be as we discussed, resulting in 0 patches or any copy actions 👍 Some MM components are more straightforward to override than others.

Also, the task do all of the import replacing takes ~1.25 seconds or so, so gulp dev is not slowed down by much.

updates made

[ryanml]

These two (mapStateToProps and mapDispatchToProps) were not exported in the MM component so they are included here.

[bbondy]

nit: BraveHome.propTypes.batTokenAdded