ENH: Ensure RAM parameter is used by persistent filters (should be applied likewise for all applications)

BUG: Actual number of threads may be less that GetNumberOfThreads() if requested region has nb lines < GetNumberOfThreads()

This reverts commit 51d5fbc5.

The "count-insert" idiom is an antipattern that leads to searching the
element twice. Avoid that and also the 0 comparison a bit below.

In addition, cache the end iterators of the two maps. This is safe as
the iterators stay valid when the map is modified.

BUG: Fix trailing whitespace trimming in otbApplicationLauncherCommandLine (kindly provided by Laurentiu Nicola)

std::string::find_last_not_of() returns a position, while std::string::substr takes an offset and a length. Fix the length computation and also add a comment regarding whether cleanStart must be checked.