Can use ASC 2.0 for AIR projects; Can make AIR libraries; Framework linkage fixes

This is a bigger commit than my previous ones, but adds more stuff too :)
Main changes:   
- Pure AS AIR apps/lbraries use the ActionScript 2.0 compiler. (maybe web projects would compile too if they don't have mxml)
- It is possible now to make .swc files that have AIR code
- Pure ActionScript AIR projects don't need the Flex framework as dependency
- The framework linkage logic was quite buggy for non-Flex projects, now it should work well

I'm making some comments in the code to make it more clear.

You can add the AIR SDK + Compiler dependency quite easily:   

     ivy {
            name 'Adobe Air SDK'
            artifactPattern Os.isFamily(Os.FAMILY_WINDOWS) ?
                'http://airdownload.adobe.com/air/win/download/[revision]/[module]_Compiler.[ext]' :
                'http://airdownload.adobe.com/air/mac/download/[revision]/[module]_Compiler.[ext]'
        }
    }
    dependencies {
        airSDK group: 'com.adobe', name: 'AIRSDK', version: '15.0', ext: Os.isFamily(Os.FAMILY_WINDOWS) ? 'zip' : 'tbz2'
    ...

Only in case of a pure actionscript project that only uses the AIR SDK you'd need to load the config (as you do now in addFramework. In all other cases we want to skip the super's addFramework code
   
    if (!flexConvention.usesFlex() || flexConvention.type.isAir()) {
        add CompilerOption.LOAD_CONFIG, flexConvention.configPath
    }