Upgrade to Java 8 (drop support of AEM 6.1)

[kwin]

To leverage classes like java.util.Base64 we should compile for Java 8. Java 8 is the minimum supported Java version since AEM 6.2. Also AEM 6.1 is out of support since quite a while now (https://helpx.adobe.com/support/programs/eol-matrix.html) so at the same time we should increase the minimum supported AEM version to AEM 6.2 (or newer).

[tomasalmeida]

Hi, should the develop branch code be jdk 1.7 compliant? I was trying to compile the code locally and it imports some java 8 lib classes (they are not used).

[kwin]

It should be according to the prerequisites in the readme. Please create a new issue to restore Java 7 compatibility.
Update: I prepared #414 to check API compatibility with Java 7.