Use meterpreter dns resolve

This replaces instances of getaddrinfo in post modules in favour of the meterpreter 

Some issues that this threw up:
a) We have a recon folder, but lots of 'recon' takes places in gather/enum_xxx... This really should be standardized? As a starting point I have moved resolve_hosts into recon...
b) enum_computers and computer_browser_discovery both use the same method but one goes via command line ```net``` and the other goes via railgun netapi calls. I have started to put together a library for netapi in https://github.com/rapid7/metasploit-framework/pull/2107. This could be expanded and alternatives for shell access via the command line could be incorporated.
c) I've deprecated the resolve_hostname module. This does have more functionality than the resolve_hosts module so perhaps should keep it? And just remove/deprecate resolve_hosts? I didn't realise it even existed tbh...
d) Some of these modules may be able to take advantage of resolve_hosts. This performs a single request, rather than multiple requests, to resolve multiple hosts and increases the module performance.

This is more to spark some comment before going too far forwards. The code could be cleaned up further. I have just tried to replace the railgun calls and keep the return/variables the same.

## Verification
- [x] post/multi/gather/resolve_hosts resolves IPv4 addresses
- [x] post/multi/gather/resolve_hosts resolves IPv6 addresses
- [x] post/multi/gather/resolve_hosts takes hostfile input
- [x] post/multi/gather/resolve_hosts takes csv input
- [x] post/multi/gather/resolve_hosts takes both hostfile and csv input
- [x] post/multi/gather/resolve_hosts errors if no hosts specified
- [x] post/multi/gather/resolve_hosts ignores empty lines and 'value, ,value'

- [x] post/windows/gather/credentials/enum_cred_store.rb still works
- [x] post/windows/gather/credentials/epo_sql still works
- [x] post/windows/gather/enum_computers still works
- [x] post/windows/gather/enum_domain still works
- [x] post/windows/recon/computer_browser_discovery still works
- [x] post/windows/recon/resolve_hostname still works and is deprecated