Add const qualifier to functions that require them

[Paolo Brandoli]

Many functions in the data handler and buffers could have const qualifiers, specially where string and pointers are used (and pass them by reference).

This avoid useless increase/decrease of the reference counter in pointers, and useless copy of strings when calling functions.

[Paolo Brandoli]

- Fixes #55 for the dataHandlers and base objects

→ ce901d8b15d7

[Paolo Brandoli]

- Fixes #55 (Add const qualifier to functions that require them) - Fixes #56 (The external lock in baseObject may create circular references)

→ 68dd9d093fad