Minimize the memory consumption when uploading images

[jokalli2]

Image upload is very memory consuming because of the image data is sent inside XML as base64 encoded. We should make sure that no extra memory allocations are made and that buffers are preallocated to sensible values, so that too large allocations cannot happen.

Some kind of reproducible test case would be nice. I will ask Peter about that.

[petertennekes]

Let's have a look at this when I return for the testcase. Maybe we should also see if we can have some check to see if the image is not to big and if it is ask to user resize or skip the upload,

[jokalli2]

The implementation is now complete, but there have been reports that uploading multiple images fail. This seems to be not related to the memory consumption. Let's investigate that as well.

[tmar]

Commits r201 and r202 change image uploads to use a single preallocated buffer, and should help with this.

I haven't tested on s60 or the more memory-constrained devices, but lacking a 'testing' status, I'll mark this as fixed. Reopen if it's still an issue.