WAB Portal Properties

Hey Miguel,

I'm in the process of re-adding the WAB property descriptions you wrote that were torn out in this [commit](https://github.com/liferay/liferay-portal/commit/707015659ec64802ac40b6f0592a1655b4361f88). Could you review what I've currently added back to make sure it's accurate?

Also, I intentionally left out the following documentation you had written:

```
#
# Use the following pattern to add custom headers to generated WABs. The
# header/value format is BND (http://www.aqute.biz/Bnd/Format):
#
#    module.framework.web.extender.headers.<header>=<value>
#
# These headers will be added to all WABs generated by the system. However,
# It's possible to target a specific WAB by appending a suffix to the
# property containing the WAB's bundle symbolic name, enclosed in brackets:
#
#    module.framework.web.extender.headers.Import-Package[my-hook]=
#
```

This was not associated to a specific property directly. Is this info independent of any WAB property in `portal.properties`? Are the sample properties you've specified above new properties that a user could add into their own `portal-ext.properties`? I'm unclear as to how this works.

Feel free to send any edits you feel are necessary back to me. Thanks! :smiley: 

https://issues.liferay.com/browse/LRDOCS-1103