Added new static checks

Added the following checks:
<ol>
  <li>Check for <code>@Inject</code> on a <code>final</code> field</li>
  <li> Validate the use of scoping annotations
    <ul>
      <li> error if a scoping annotation is anywhere but a class or method </li>
      <li> error if a scoping annotation is on an abstract class or interface </li>
      <li> error if more than one scoping annotation is on an element where scoping is allowed </li>
      <li> warning if a scoping annotation is on a method that is not a <code>@dagger.Provides</code> method </li>
    </ul> 
  </li>
  <li> Validate the use of qualifier annotations
    <ul> 
      <li> error of more than one qualifier annotation is on an element where qualifiers are allowed (this check was already present; I just moved it.)</li>
      <li> error if a qualifier is anywhere but a field, method, or parameter </li>
      <li> warning if a qualifier is on a non <code>@dagger.Provides</code> method </li>
      <li> warning if a qualifier is on a parameter that is not a <code>@dagger.Provides</code> method parameter or an <code>@Inject</code> constructor parameter </li>
      <li> warning if a qualifier is on a non-injectable field </li>
    </ul> 
  </li>
  <li> Check that <code>@Provides</code> methods are only declared in modules</i>
</ol>

Warnings for misuse of qualifiers can be suppressed with `@SuppressWarnings("qualifiers")`, and warnings for misuse of scoping annotations can be suppressed with `@SuppressWarnings("scoping")`.

Also, take a look at <a href="https://code.google.com/p/error-prone/">error-prone</a>, where I've added lots of general DI checks. The checks in error-prone and here overlap largely, but there are a few that are only in error-prone. For example, I've written error-prone checks to fail if scope and qualifier annotations do not have runtime retention or if a scoping annotation has invalid targeting. (Not all of these checks have been merged into the main error-prone project yet, but if you want to take a look at what's coming, they're all in <a href="https://github.com/sgoldfed/error-prone">my error-prone fork</a>). Also, error-prone has the benefit that it will do the static checks for all DI frameworks.