feat(chromium meta): generate manifest.json using gulp

- add source/meta/chromium-manifest.json which is a Lo-Dash template
- add gulp "meta" task which compiles that template and writes
result to builds/chromium/manifest.json
- run "meta" task in "default" task
- ignore builds/chromium/manifest.json

This is related to #43.
fix(opera): take .gitignore out of extension folder
feat(firefox meta): generate meta files using gulp

- add source/meta/firefox/install.rdf and chrome.manifest
which are Lo-Dash templates
- in gulp "meta" task compile them to builds/firefox
- ignore these files in builds/firefox
- change Firefox add-on ID to happy@deltaidea as it is more clear

This is related to #43.

IMPORTANT: Manually remove previous version from Firefox as this
commit changes Firefox add-on ID.