Adds string utility class

At this time only supports a static method to create empty strings.
Enhances xml publisher parser

Moved parsing of creation and update dates into XmlParserUtil.
XmlPublisherParser will now skip tags if no <publisher> tag was read.
Updated test accordingly.
Moves parsing of id's to XmlParserUtil
Adds XmlParserUtil.textOf() utility method to extract text

This method removes any unwanted whitespaces from xml texts.
Adds event xml parser and tests

Note: publisher modified to make Publisher.equals() method similar to
Event.equals() one.
Adds "throws DaoException" to method signatures of dao interfaces
Changes visibility of parsing methods to public
Refactors parser to parse one entity or multiple entities
Fixes pom.xml build file encoding
Adds Arrays utility class

This utility class is able to create arrays of any type by invoking
Arrays.from().
Adds implementation for event daos (content and http)

Updated SqliteOpenHelperV1 to create a table to store events.

Note: modified PublisherContentDao that its implementation is similar to
the one of EventContentDao.