remove direct dependency on thin as the rack implementation

[tempredirect]

the main reason for this is to allow compatibility with jruby as thin is not really compatible out of the box with jruby.

the change basically removes thin from the dashing.gemspec file and moves it to the dashboard's Gemfile where it is wrapped in a platform :ruby block and instead of using 'thin start' it uses 'rackup' to start the server.

initial problems:

• current projects may revert back to webbrick on up grading as there Gemfile won't have been changed
• the dashing stop command assumes 'thin' as there doesn't seem to be an equivalent rackup, guess may have to use the rack.pid file and kill the process

[davefp]

I like this. Giving users the ability to use the app server of their choice is a great addition.

Because of the breaking changes it'll have to be part of a 2.0.0 release though, so I may not merge it in for a while. It will also be dependent on fixing the dashing stop command.

[theigl]

+1

[ledesma]

+1

[ducky427]

+1

[padi]

+1

[terraboops]

This PR can be closed as it is superseded by #427 -- hopefully that one is merged soon.

[pushmatrix]

Yeah, moving all discussion to #427 for now