hildongui: Fix: short description not shown (if no-use-html)
disable debug message
Fix: there are images without dot in filename, they run out of range
If image can't be loaded: use logger.error, not logger.exception
downloader: additional error case checking
downloader: common set out from if-elif -branches
downloader: retry three times in network issues (e.g. timeout is typically working on the next try)
cachedownloader: Errors with networking (e.g. timeouts) is not crashing anymore, but returning None
downloader: add more different errors (on networking)
downloader: return None at the end of the function
downloader: automatic close after read
downloader: After urlopen but before checking if content is gzipped, check errors (None returned)
cachedownloader: Use read_from_network for all reading
core: Use read_from_network for reading over network
cachedownloader: check more if network reading returns None
downloader: Fix: error checking in wrong place
downloader: defaulttimeout=15 (it was 30, but now there are retries)
downloader: Catch http-errors. Fix #163
downloader: String 'User-Agent' duplicated in header. FIX #171, FIX #174

Links/images on caches/logs point another servers, and some of them are nitpicks.
Fix #177

_get_fieldnotes_button should not call timeconsuming update_fieldnotes_display
'fieldnotes-changed' calls it (and it happens also during startup)