Add support for timestamp type to formulas

[Nicklas Nordborg]

As a side-effect of #1512 and it's propagation to extended properties formulas can now also return timestamp values. The option is already present in the gui when creating a new formula. But it will create a date instead of a timestamp when used. A fix is needed to make various listings display a timestamp. We should also check if the various exporters can handle it. The table exporter currently throws an exception:

java.io.IOException: java.sql.Timestamp cannot be cast to java.lang.Number
at net.sf.basedb.clients.web.plugins.SimpleExport.exportProperties(SimpleExport.java:656)
at net.sf.basedb.clients.web.plugins.SimpleExport.performExport(SimpleExport.java:362)
at net.sf.basedb.core.plugin.AbstractExporterPlugin.run(AbstractExporterPlugin.java:144)
at net.sf.basedb.core.PluginExecutionRequest.invoke(PluginExecutionRequest.java:116)
at net.sf.basedb.core.PluginExecutionRequest.run(PluginExecutionRequest.java:141)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassCastException: java.sql.Timestamp cannot be cast to java.lang.Number
at net.sf.basedb.util.formatter.NumberFormatter.format(NumberFormatter.java:33)
at net.sf.basedb.clients.web.plugins.PlainTextTemplate.writeProperty(PlainTextTemplate.java:123)
at net.sf.basedb.clients.web.plugins.SimpleExport.exportProperties(SimpleExport.java:634)
... 5 more

[Nicklas Nordborg]

(In [5440]) Fixes #1522: Add support for timestamp type to formulas

List pages with formulas now use the proper formatter (added FormatterFactory.getFormulaFormatter) which builds on the value type of the formula. The problem wih the table exporter was not actually related to the timestamp... but to a hard-coded Type.FLOAT value type for all formulas.

Other exporters (BaseFileExporter and BfsExporter) doesn't use formatters at all.