syntax refactor

[wuliupo]

Only syntax refactor,

1. remove unused return null;
2. a in b write in b.a will more clear;
3. wrappers only have one property helper;
4. _restore and _destroy were simplified as delete item.sortable.

[coveralls]

Coverage decreased (-0.6%) to 99.383% when pulling b68ae26 on wuliupo:master into 4bb4493 on angular-ui:master.

[thgreasi]

I'm totally in favor of 'use strict', but this might cause errors in some ASP.Net environments.
jQuery prior v3 also didn't use 'use strict' for exactly that reason.

[wuliupo]

Okay, I remove this line! Thanks!

[coveralls]

Coverage decreased (-0.6%) to 99.383% when pulling 8e728b4 on wuliupo:master into 4bb4493 on angular-ui:master.

[thgreasi]

That's not equivalent in case of directiveOpts members with falsy values.

[thgreasi]

Please don't create a hure diff. Try not moving methods until the initial refactor gets reviewed.
Keep in mind that targeting the absolute min number of code lines can hurt the debug-ability of the code. Also refactoring chained method invocations to be in the same line can hurt the readability of the code.