Fixed interval constant "hour"

The interval string “hour” had a typo: “houre”.

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Fixed Issue with date during convertProperties call in the update function.

Added more update-options
Revised try/catch blocks

Add new interface methods like exists, getIds, get

Close issue #38

Changed add-,cancel-, and clear function
Revised class-structure

fixed iOS 8.1 build fails with linker error #365

There was a copy paste error in the plugin.xml. That's why 2 files were not compiled.