Various improvements

Improvements:

• Text panels no longer fixed height (#52)
• Report timezone determined by server. Thanks to @thnurg for investigating (#43)
• Set filename and extension to use when downloading file. (#62)

Thanks to the following contributors for their fixes:

• @Flowm for fixing timestamp parsing on 32bit systems (#54)
• @jkreileder for fixing relative time specifications to include also work for positive relative time (#71)
• @vryzhaiev for fixing the docker build and adding ca-certificates to the docker image (#74)