Change ContentSensor.empty() to ContentSensor.isEmpty()

To avoid confusion between the action of emptying and checking if
contents are empty
Add Sharbal entity and turn physics drawing back on
Add a sensor to Sharbal

To detect duck and tell it to go away
Test out Sharbal with a cereal box
Generate phrase from a String[] when talking

Can be set by constructor, otherwise uses default phrases
Remove washing machine temporarily

so that Sharbal phrases can be seen completely
Make quacking boolean public

So that Sharbal can access it
Sharbal will respond to duck's quacking

Also increased sensor size
When duck quacks inside sensor, a new task is scheduled to say a random
phrase in response
Sharbal should say 'ouch' when hit by an object with certain velocity

Not yet functional
Error found: when duck flies inside sharbal's sensor, a new phrase is
generated, which shouldn't happen
Cancel old respond task if a new response is reqeusted

So that when duck quacks a lot, there won't be a ton of responses. Just
one.

Commented out speech when duck enters sensor because it might not be
necessary.
Fix Sharbal sensing being hit

Needed to use contactee instead of entityFixture
Both objects in contact are technically contactees and entityFixtures,
this is confusing!
Use actual sharbal image
Properly position Sharbal

The only issues that appear to remain are:
1. Sharbal is not rendered on top of other entities, so text is
sometimes unreadable
2. When sharbal detects getting hit, often it is detected multiple times
and multiple "ouch" messages are made
Extract painful velocity limit to variable

Also stop rendering physics world
Fix multiple "ouch"es when sharbal is hit

In special cases it can still happen but it's not a big deal
Finishing touches

Remove unnecessary field and comment out currently unused variable