modal directive clobbers id attributes

[lanterndev]

I just upgraded from a 0.1.1-SNAPSHOT from Feb. 19 to the 0.2.0 release, and my elements using the modal directive are now having their ids stripped.

[pkozlowski-opensource]

@Skivvies as commented in #198 I'm not sure we want to support this scenario of keeping custom ids. From what I understand you can cover your use case by specifying a CSS class.