Fixed bug in resolving of conditional Revision Aware XPath.

Fixed bug in resolving of conditional Revision Aware XPath.

Fixed implementation in TypeProviderImpl - if leafref references the leaf through the conditional XPath the method will no more returns null but wrapped Type as java.lang.Object.
Added test into GeneratedTypesTest for conditional XPath.
Fixed controller-network-ne.yang - changed name of flow-tables to flow-tables2 - the build should no more fail.
Fixed wrong transformation of yang namespace to java package in case that yang namespace contains numbers right after the "."
Added check into BindingGeneratorUtil - validateJavaPackage.
Refactored and commented SchemaContextUtil.java

Signed-off-by: Lukas Sedlak <lsedlak@cisco.com>