better customisation features for schedule component

all css classes can now be overridden using component attributes
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I have completely rewritten the examples. There are now 4 of them, each demonstrating a different feature
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the themeing mechanism has changed: instead of using the theme id to determine which css file to load, the theme id is now added to the schedule div css class as a suffix: e.g. schedule-detailed-default, schedule-detailed-outlookxp, schedule-detailed-evolution, ...
This makes it easier to use a custom theme: just copy the appriopriate content of the schedule.css file to your own css, and add a suffix to schedule-detailed and schedule-compact
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introduced the ScheduleEntryRenderer, which renders the content of a schedule entry. By writing an implementation of this
interface, it is now possible to customize what is rendered inside a schedule entry. Using this mechanism, you can now also
assign different colors to the entries of different persons. I think this is a better solution than the patch introduced by bug nr. 976. The changes to the ScheduleModel that were made here, are therefore undone with this patch
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fixed a bug in the AbstractScheduleModel that sometimes caused the schedule to contain 0 days after submitting.
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added a property to the ScheduleModel, entrySelected, which returns true if an entry is currently selected. This is a convenience
method which can for example be used in the 'rendered' or 'disabled' flag of a component.
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added methods to add and remove entries to the ScheduleModel interface.