Add EventTable type

[oruebel]

Fix #285

Add support for EventsTable

• Added new EventTable type
• Added unit tests for the new EventTable type
• Updated NWBFile to create events/ group and added NWBFile::createEventsTable convenience function

Enhance DynamicTable to improve support for use during acquisition

• Refactored DynamicTable so it creates and initializes its ElementIdentifiers id column internally during initialize(). This is to ensure the ElementIdentifiers are always create before we start the recording. Calling DynamicTable::setRowIDs() previously required creation of ElementIdentifiers but may be called later during recording. As part of this change, setRowIDs() now takes only the row ID values and writes them directly to the table's built-in id column instead of accepting a separate ElementIdentifiers object. In practice this aligns the API with the intended usage, since callers should have always used the table's own id dataset. (@oruebel, #302)
• Updated DynamicTable column-name management to be immediate and table-driven. addColumnName() now flushes new column names to the file as columns are added, setColNames() is now restricted to reordering the existing set of columns (it no longer acts as a general overwrite mechanism), and finalize() no longer writes the colnames attribute because column-name updates are persisted when they occur. This ensures that the colnames attribute is always consistent with the actual columns in the table and helps avoid creation of invalid files. (@oruebel, #304)

Other

• Fix bugs in TimestampVectorData and DurationVectorData; e.g, bad namespace and inconsistent ordering of parameters in initialize
• Update Changelog