Clean up different icons in start view

[joergreichert]

Current state: Initial start view looks overwhelming by displaying so many different icon markers.

Motivation: Start screen should appear concise and tidied up.

Future state:

• at start screen / at start zoom level, only trees are visible, pumps and other watering sources will only appear when zooming to certain level
• instead there should be overlay showing the number of different items of the current visible view
• it should be possible to click at one of the item types and then jump + zoom to the first of the items of this type, with previous and next buttons jump to the corresponding other items of that type

[joergreichert]

TODOs:

• buttons to jump to next, previous marker for a icon
• fix number calculation (because when zoomed out to wide, features are considered as not visible / not there although they are within the bounding box, so use the static initial values, when zoomed at to certain level)

Input from working group:

• use logos instead of text, so bar needs less space
• show number of registered users within a area (maybe filterable to users who actual watered the last 30 days)

Later

• show number of planned events
• show watered liters in last 30 days
• show watering groups

[joergreichert]

fixed with https://github.com/CodeforLeipzig/leipziggiesst/commit/a270a9ec3382cafdbfe27d9fd1109ca40f554dbc