support building of ios and android release artifacts

## Steps to Reproduce

1. Create a new Flutter project inside IntelliJ
1. Invoke Build > Build Project

Fails with a bunch of Android errors:

```
Information:java: Errors occurred while compiling module 'android'
Information:javac 1.8.0_72 was used to compile java sources
Information:24/04/2017, 15.28 - Compilation completed with 1 error and 3 warnings in 2s 431ms
Warning:java: source value 1.3 is obsolete and will be removed in a future release
Warning:java: target value 1.3 is obsolete and will be removed in a future release
Warning:java: To suppress warnings about obsolete options, use -Xlint:-options.
/Users/mit/tmp/test31/android/app/src/main/java/com/yourcompany/test31/MainActivity.java
Error:(10, 6) java: annotations are not supported in -source 1.3
(use -source 5 or higher to enable annotations)
```

Start by reproducing the failure from a new Flutter project created in IntelliJ and inspect how Build > Build Project invokes the Android module. Compare the Java compiler settings with the generated project configuration. Done means the project builds successfully and the requested iOS and Android release artifacts are supported.

Written by the indexing model from the issue text.