Merge file annotation writing examples into annotation section

- Improve readability of the annotation writing subsection
- Merge Updating file annotation into Writing annotations
Improve description of getImages() by container signature
Homogeneize comments across the MATLAB documentation page
Minor fixes
Remove thumbnail methods from the MATLAB documentation page
Additional fixes suggested by @jburel
Merge pull request #579 from sbesson/matlab_fixes

Matlab additional fixes