Adopt minimal Sencha Cmd package requirements

[bentrm]

This PR aims to be less intrusive than #302 while still adding support for Sencha CMD. It only adds one configuration file and some docs (which may be extended in the future).

To play nice with Cmd the following changes had to be made to the newly added package.json:

• Cmd only allows numeric version so I dropped the -dev suffix
• type needs to be set to code
• compatVersion will probably be helpful with upgrading to future versions

I tried it with an existing application (ExtJS 4.2.1) as well as with a newly generated test app (ExtJS 5.1).

[marcjansen]

Thanks for your continued work on this @bentrm.

/cc @KaiVolland I'd value your opinion on this very much (he is the expert for the sencha command).

[marcjansen]

From the diff I'd say this looks great! Let's wait for @KaiVolland's approval

[KaiVolland]

Looks good to me.

[marcjansen]

Cool. Thanks to both of you @bentrm & @KaiVolland