Explore page: display data from the opened file on the chart and arrange layout

[tadeuszbaraslupski]

The core feature of the app is the "Explore" page. It should display data from a chosen file. User will open file in this format (this file is artificially generated by @swiezew, but the format is the same):
output_corrected_groups.tar.gz

Acceptance criteria

• show basic statistics about the data like number of animals, dates range, number of sites
• show data from the loaded file on the simple chart (at the minimum show the number of animals at a given location across time)
• layout on the Explore page is arranged so that it's nice, organized and usable. Add placeholders for controls that will be needed in Explore page: add results filtering #46 that will filter data based on the values in columns (date from-to selection, species multiselect, site/"check" multiselect).