Move to gradle wrapper fdroid wants

Merge pull request #600 from SamWhited/gradle

Build system and library changes (Gradle / Subtree merging)

Merge branch 'gradle' into development

Conflicts:
	.gitignore
	CHANGELOG.md
	README.md
	libs/MemorizingTrustManager
	libs/minidns
	libs/openpgp-api-lib

Use Gradle build system