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.