do ProtocolEvents fixing only when there is required fields missing in the requested schema

https://issues.apache.org/jira/browse/PARQUET-61
This PR is trying to redo the https://github.com/apache/incubator-parquet-mr/pull/7

In this PR, it fixes the protocol event in a more precise condition:
Only when the requested schema missing some required fields that are present in the full schema

So even if there a projection, as long as the projection is not getting rid of the required field, the protocol events amender will not be called.

Could you take a look at this ? @dvryaboy @yan-qi

Author: Tianshuo Deng <tdeng@twitter.com>

Closes #28 from tsdeng/fix_protocol_when_required_field_missing and squashes the following commits:

ba778b9 [Tianshuo Deng] add continue for readability
d5639df [Tianshuo Deng] fix unused import
090e894 [Tianshuo Deng] format
13a609d [Tianshuo Deng] comment format
ef1fe58 [Tianshuo Deng] little refactor, remove the hasMissingRequiredFieldFromProjection method
7c2c158 [Tianshuo Deng] format
83a5655 [Tianshuo Deng] do ProtocolEvents fixing only when there is required fields missing in the requested schema
PARQUET-63: Enable dictionary encoding for FIXED.

This uses the existing dictionary support introduced for int96. Encoding
and ParquetProperties have been updated to use the dictionary supporting
classes, when requested for write or present during read. This also
fixes a bug in the fixed dictionary values writer, where the length was
hard-coded for int96, 12 bytes.

Author: Ryan Blue <rblue@cloudera.com>

Closes #30 from rdblue/PARQUET-63-add-fixed-dictionary-support and squashes the following commits:

bc34a34 [Ryan Blue] PARQUET-63: Enable dictionary encoding for FIXED.