Create list of dependencies (`cpanfile` format)

[book]

Create a file in cpanfile format containing all the required modules to run CPAN.io.

The current list is:

• BackPAN::Index
• DBIx::Class
• DateTime
• Path::Class
• Plack
• Template
• Text::Markdown::PerlExtensions
• Web::Simple

[book]

New dependency:

• Git::Repository