Linting fixes and simplification

These changes fix issues detected by JSHint and simplify expressions to increase readability.

Fixed linting issues (96 in total, jshint@2.7.0):

• Accidentally globally defined variables
• Redefined variables
• Typo in identifier name
• Duplicate object key
• Coercing equal
• Confusing negation of 'lesser than' comparison
• Undefined globals from libraries
• Missing blocks for conditions
• Functions defined inside of loops (performance)

Simplified expressions:

• Check for thruthy/falsy values when possible instead of type checking against 'undefined'
• Use logical OR for fallback values (instead of x = x ? x : y;)
• Remove explicit type conversion in conditions (if (!!x)) and in places where the variable already is a boolean
• Replace ternary IF with a boolean result by the condition itself
• Refactored:

  if (newValue === 0 &&
      typeof this.someProperty === "undefined" ||
      newValue === this.someProperty) { }

  to:
  if (newValue === (this.someProperty || 0)) { }

Minor code style fixes:

• Indentation
• Capitalization

Removed code:

• Obsolete commented out code
• Code for IE < 4 and NS < 6 (really! 😀)