[rfc] addons: allow building addons with type different than xbmc.python.scrip...

this will allow us to build not only 'xbmc.python.script' addons but also 'xbmc.python.module', or whatever is supported by kodi - just drop an "addon template" in config/addons if you want new type of addon..

I have tested already converting Cheetah package (in unofficial) to a module. a test addon that requires Cheetah works fine
```
openelec:~/.kodi/addons/test.test # cat addon.xml
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<addon id="test.test"
       name="test"
       version="4.3.2"
       provider-name="poof">
  <requires>
    <import addon="os.openelec.tv" version="5.0"/>
    <import addon="xbmc.python" version="2.1.0"/>
    <import addon="script.module.openelec.Cheetah" version="0.0.0"/>

  </requires>
  <extension point="xbmc.python.script"
             library="default.py">
        <provides>executable</provides>
  </extension>

  <extension point="xbmc.addon.metadata">
    <summary>test</summary>
    <description>test</description>
    <platform>all</platform>
  </extension>
</addon>
openelec:~/.kodi/addons/test.test # cat default.py
import Cheetah
from Cheetah.Template import Template

templateDef = """$contents"""
nameSpace = {'contents': 'Hello World!'}
t = Template(templateDef, searchList=[nameSpace])
print t
```

thoughts?