Complete review of metadata

@DimEvil have a look at 8d2b02b04f84bdd7f60c6038db56750c975d745c to see my changes in the metadata. It has already been updated as such on the IPT, but with GitHub, we know have the original text too.

Main changes:

* Corrected typos
* Dropped resource citation and purpose (until we have a data paper)
* Standardized abstract (until we have a data paper)
* Rephrased design description, with less focus on the VIS application **Please check**
* Rephrased additional information
* Added some numbers to taxonomic description
* Dropped intermediate taxon levels, kept kingdom, class and families
* Reduced geographic coverage description: coordinate precision is now (only) discussed in study extent description
* Used precise time range (otherwise it appears as 2012-01-01 on IPT)
* Reduced study extent: goal of research is mentioned in Design description
* Focused sampling description on sampling methods only (not on area) **Please check**
* Split up method step description in separate steps, with consistent format. **Please check**
* References: Used `,` between authors and add  `.` at end.