Flexible meteor shower list

[Molau]

Currently I can select only showers from a pre-defined shower list.

In the future, meteorflux should offer me all showers which are found in the uploaded flux data. If the shower is stored in the shower list, it shall be displayed with the stored begin/end dates and population index. If it´s an unknown shower, the begin and end dates should be left free (I have to fill them in before the plot is generated) and the population index should be set to 3.0 as default