Expose db and pcap groups as gems

Add `metasploit-framework-db.gemspec` and use it in the `db` group in the `Gemfile`.  Likewise, add `metasploit-framework-pcap.gemspec` and use it in the `pcap` group in the `Gemfile`.  Add a `metasploit-framework-full.gemspec`, which depends on `metasploit-framework`, `metasploit-framework-db`, and `metasploit-framework-pcap`.  `metasploit-framework-full` can be used in Pro instead of `metasploit-framework` to ensure that Pro's version constraints on db and pcap gems are compatible with the version constraints in metasploit-framework.  This should prevent incompatible versions of `metasploit_data_models` and `metasploit-credential` between `metasploit-framework` and Pro.

# Verification Steps

## specs
- [ ] `rake spec`
- [ ] VERIFY no failures

## cucumber
- [ ] `rake cucumber`
- [ ] VERIFY no failures

## Without db
- [ ] `bundle --without db`
- [ ] `bundle list`
- [ ] VERIFY `activerecord` is NOT in the list
- [ ] VERIFY `metasploit-credential` is NOT in the list
- [ ] VERIFY `metasploit_data_models` is NOT in the list
- [ ] VERIFY `pg` is NOT in the list

## Without pcap
- [ ] `bundle --without pcap`
- [ ] `bundle list`
- [ ] VERIFY `network_interface` is NOT in the list
- [ ] VERIFY `pcaprub` is NOT in the list

## Without nothing
- [ ] `bundle --without ''`
- [ ] `bundle list`
- [ ] VERIFY `activerecord` is in the list
- [ ] VERIFY `metasploit-credential` is in the list
- [ ] VERIFY `metasploit_data_models` is in the list
- [ ] VERIFY `pg` is in the list
- [ ] VERIFY `network_interface` is in the list
- [ ] VERIFY `pcaprub` is in the list
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