Add messaging when selecting county/blockgroup containing locked block

[pcaisse]

Overview

Add messaging when selecting county/blockgroup containing locked block

Acceptance Criteria

• A toast message should be shown to the user specifically when a selection is only partially successful (or not at all) due to the geounit(s) containing locked blocks
• The message should read: Unable to select areas that contain locked blocks
• The message should also contain a link to the docs at https://github.com/PublicMapping/districtbuilder/wiki/Block-Editing

Notes

This is needed because we've decided to not allow for partial selection that would result in selecting blocks since block selections are not available at all geolevels (see #323 (comment)).

Here is the direction from UX:

For blocks, we are okay with handling them differently, since they are a more advanced part of the tool. For these, we should show a toast message when we are unable to make a selection due to locked blocks. We should throttle the message or find another way for it not to appear over and over if the user is selecting with the rectangle tool