Show dropdown above the host element if below there is not enough space available

[web-party]

Currently, the dropdown seems to always open below the "host" element so that in some cases the dropdown becomes partially hidden.

select2 uses the following mechanism to detect if there is room available below or above:
https://github.com/select2/select2/blob/0a30b0b3e67843c09b0bcc4d01e65b72d9b1279f/src/js/select2/dropdown/attachBody.js#L151-L179

[web-party]

Realized that it's a duplicate of #283 and #163.