explorer: provide capa insight via "hint" popups

[williballenthin]

IDA plugins can override the "hints" displayed to a user when they hover over an address. By default, this displays the first few lines of disassembly. We could override this behavior and provide a summary of the function's capabilities, via the capa rule matches.

Example of the implementation is here: https://github.com/williballenthin/idawilli/blob/master/plugins/dynamic_hints/dynamic_hints.py

[williballenthin]

note that we wouldn't want to override this behavior if the user doesn't want it. so there would need to be some configurable setting.