Merges branch 'release/1.6.0' into develop
Adds Localization API.

To localize a plugin use,

```php
<?php
function localize() {
  $this->__('Foo string to localize');
}
```

The `local` localization helpers are `_`, `__` and `t`. These are
aliases to the `translate` method. The `translate` method takes a string
and localizes it using the WordPress `__` api method.

The text domain of a plugin is assumed to be the same as it's slug by
default.
Improves localization tests.
Adds `pluginVersion` to saved options and Fixes failing test.
Adds `pluginVersion` to OptionsStore.

* PluginMeta gets the `needsUpgrade` helper that can autodetect if the
  plugin needs to be upgraded.
* Any required schema migration should be done behind `needsUpgrade`.
Merges branch 'feature/add-plugin-version-to-options-store' into develop
Updates changelog.
Adds test for `Sentry#getRequestParams`.
Adds test for abstract api.
Adds test for Validator abstract api.
Improves code coverage
Merge branch 'feature/improve-code-coverage' into develop
Updates changelog
Bumps version to 1.7.0.
Updates changelog for 1.7.0.
Merges branch 'release/1.7.0'