Miscellaneous uninitialized variables cleanup

[benlk]

Changes

• Fixes Undefined Index: lazyLoad in widget
• Fixes visibility problem for widget constructor
• Fixes a weird error on first save of settings:
• Fixes https://github.com/INN/doubleclick-for-wp/issues/37
• Maybe fixes https://github.com/INN/doubleclick-for-wp/issues/8, specifically the part that puts a PHP Notice in the value of one of the inputs.
• Slaps a big todo in dfw-options.php for improving the array. Will spin that out into a new issue for later work.
• Sets the text-domain to 'dfw'; we've had the text domain in use earlier but it wasn't defined anywhere.
• Some code-style cleanup
• Adds license, license URI to plugin header
• Updates author URI to labs.inn.org

Testing/Questions

Questions that need to be answered before merging:

• [x] Do settings saved in previous versions of this plugin still work in this version of the plugin?

Steps to test this PR:

1. Save settings using an old version of this plugin, 0.2.1.
2. Check out this branch
3. Do the settings on the settings page match what they previously were?

[benlk]

Tested during development; merging.