Support field renaming for Avro read schemas, by means of
field aliases.

Avro 1.7.6 is required since it fixes https://issues.apache.org/jira/browse/AVRO-1433
But note that this is only to allow the test to run correctly.

Conflicts:
	parquet-avro/pom.xml
Add explicit blank namespaces to account for change in AVRO-1295 in Avro 1.7.5.
Don't shade Jackson since Avro exposes Jackson classes in its public API for representing default values for fields.
Added ParquetWriter() that takes an instance of Hadoop's Configuration.

Conflicts:
	parquet-hadoop/src/main/java/parquet/hadoop/ParquetWriter.java
first use current thread's classloader to load a class, if current thread does not have a classloader, use the class's current classloader to load a class.
This will make sure a class not packaged in parquet but on classpath loaded properly. Otherwise, for example, if you set your own ReadSupport class to the
Configuration object and expect it to be loaded by ParquetInputFormat, it will fail and throw ClassNotFoundException.
use utility method from Configuration class to load class to avoid ClassNotFoundException