Enabling accessibility and resetting simulator content and settings in Xcode 6 simulators

## motivation

Automatically enables Accessibility on Xcode 6 simulators.

The spec/run_loop_spec demonstrates:

1. reseting the simulator content and settings, and
2. launching an app on a simulator in Xcode 5.1, 5.1.1, and 6.0.

## notes

In Xcode 5, calabash-ios function `reset_sim_content_and_settings` resets the content for every simulator, regardless of SDK.

In Xcode 6, we have option of reseting just the contents and settings of a particular simulator.  I believe that we should have two behaviors: one that resets _all_ simulators and one that resets specific simulators.  Resetting all the simulators takes a long time and resetting individual simulators is the direction that Apple would like us to go.

From the beta release notes [1]:

> **Configurations.** New iOS Simulator configurations allow you to keep data and configuration settings grouped together. Run one configuration for one version of an app, with its own data, and another configuration for a different app version.

## tests

```
# testing against Xcode 5.0, 5.0.1, 5.0.2, 5.1, 5.1.1, 6b4
# some tests are skipped for Xcode < 5.1 - gotta draw the line somewhere.
Finished in 1 minute 21.51 seconds (files took 2.09 seconds to load)
110 examples, 0 failures
```

#### noteworthy  tests

```
RunLoop
  .run
    on simulators
      using Xcode '/Xcode/5.1/Xcode.app/Contents/Developer'
      using the current version of Xcode
      using Xcode '/Xcode/5.1.1/Xcode.app/Contents/Developer'
```

## links

- [1] [beta 5 release notes](http://adcdownload.apple.com//Developer_Tools/xcode_6_beta_5_za4gu6/xcode_6_beta_5_release_notes.pdf)