Only delete remote files when necessary with theme watch command

Because files that are present locally overwrite remote files anyway,
it is not necessary to delete all files on every execution of `theme
watch`.

Only files that are not present locally are deleted on the remote side.
Speeds up the command extraordinarily in projects with tons of assets
(-> nearly all projects).
See pull request #21 by joelongstreet

Fix 'errors_from_response'

https://github.com/Shopify/shopify_theme/pull/21

I hope the project owner is still active…
Use api over https
Adding ICO to the list of recognized binary files will prevent an exception being thrown when trying to upload an ICO file
Syck is removed in Ruby 2.0
Uses Listen in blocking mode, and adds the version to the gemspec.
Merge pull request #31 from keichan34/add-ico-to-binary-files

ICO files cause errors
Merge pull request #32 from keichan34/supress-syck-warning

Syck is removed in Ruby 2.0
Merge pull request #33 from keichan34/29-theme-watch

Uses Listen in blocking mode, and adds the version to the gemspec.
Merge pull request #25 from dlindenkreuz/master

Only delete remote files when necessary with theme watch command
Merge upstream changes from shopify repo