Add URLEscaper

See #504 .

* add com.google.gdata to use PercentEscaper
* add function in morph to encode item
* add morph function description
* add schemata used to include morph function
* update test file
Judging from https://github.com/hbz/lobid/pull/31 we don't need the additional `com.google.gdata` dependency, since `com.google.gdata.util.common.base.PercentEscaper` seems to be in Guava 15.