Clean-up .clang-tidy and apply camelBack case on functions and variables for some modules

[cbentejac]

Description

This PR updates the .clang-tidy file to detect instances where the case used for a variable/function/class/structure differs from the following:

• camelBack for functions and variables;
• CamelCase for classes and structures.

Using that file, the following modules have been updated to respect these rules:

• sfmDataIO: in particular, the Load/Save functions have been renamed to respect camelBack case
• image: in particular, accesses to the width and height, which are used across all the project, have been renamed to respect camelBack case; "convertion.hpp" and "convertionOpenCV.hpp" have also been renamed to fix the typo in the filenames
• sfm: functions as well as variables within these functions' definitions have been heavily renamed to respect camelBack case

The modifications are not exhaustive and do not fix all the warnings generated by clang-tidy but intend to start harmonizing globally the code.

This pull request presents no functional change.

This relates to alicevision/QtAliceVision#66.