Build WAM demo applications from sources

Close for FF 6.0.4 and GG 7.0.0

A recipe following the requirements of this ticket has been submitted to: https://github.com/webosose/meta-agl-lge/pull/33

Already received some feedback on how to best manage the different demos packaged by the recipe. Will also submit to AGL gerrit when we pass this early review process.

Created a Makefile that makes use of wgtpkg-pack like this:
{{$ cat Makefile
APP_LIST=annex hvac-enact memory-match youtube

package:
mkdir -p package
for i in $(APP_LIST); do \ wgtpkg-pack $$i -o package/$$i.wgt; \ done

.PHONY: clean
clean:
rm -rf package
}}
Unfortunately, in the case of one of the apps, hvac-enact, it doesn't package all the files.

{{$ diff -r hvac-enact/ hvac-packaged/
Only in hvac-enact/: appinfo.json
Only in hvac-packaged/: hvac-enact.wgt
Only in hvac-enact/: main.js
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: aa
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: ab
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: abq
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: ach
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: ada
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: ady
Only in hvac-enact/node_modules/@enact/i18n/ilib/locale: ae
...}}

Sample app sources temporarily hosted at: https://github.com/jaragunde/wam-demo-applications

Recipes would be very simple. The `aglwgt` bbclass is provided, it relies on the app to provide a `make package` target, that creates the .wgt file under the `package` directory. A tool called `wgtpkg-pack` is provided for that purpose. If the `package` target, exists the recipe only has to point to the app sources.

And since these are web applications, no compilation is involved, we only have to package the app/widget.