Add channel selection on Fee Rate page

[Bitcoinite]

Currently we have the possibility to batch change fees for several channels using the Update Channel Policy table on the Dashboard. Since it looks like nobody is using this feature, I suggest we remove it from the Dashboard and instead add this functionality to the Fee Rates page. This is the place where users would look out for such a feature.

So I suggest to add the following:

• Add checkboxes to select channels on the Fee Rates page
• Add Label and Input fields to change the fee rates for all selected channels at once on the Fee Rates page