Optional max size for downloading images and increase timeouts
- A plugin that uses download function in gajim cannot download files larger than 2MiB.
- Timeouts can occur on mobile network
- Limit set to 2MiB in get_img* in helpers.py
- Several different timeout limits are set in get_img* in helpers.py
See attached patch by tmolitor. File size limit can now be set as an argument when calling function download_image.