GUI: More concise text for length settings

See merge request !425

Simplify name of config subdirectory

See merge request !424

MultiOption: Replace `boost/variant` with `std::variant`

The dependence of `Fit/Tools/MultiOption` on `boost/variant` and `boost/lexical_cast` is removed in favour of `std::variant`.

Instead of Boost's `lexical_cast`, the C++ `std::to_string` is used and due to the change in the output for doubles, the test `Fit.Unit.MinimizerOptionsTest.toOptionString` is updated.

See merge request !422

Device/Mask: Mark the Boost functions by using the explicit namespace

See merge request !423

Instead of Boost's `lexical_cast`, the C++ `std::to_string` is used
and due to the change in the output for doubles, the test `Fit.Unit.MinimizerOptionsTest.toOptionString` is updated.

After removing the dependence on Boost, the following files are updated:
- OptionContainer
- MultiOptionTest
- Report: Update according to latest changes
- MinimizerFactory
- MinimizerOptions

The used functions from `boost/geometry` are marked by using `boost::geometry`
namespace in order to make clear which functions are used from the Boost library.
This conforms also with the other parts of the codebase, eg.,
`Device/InputOutput/boost_streams`.

Unneeded included headers are removed.

AlQuemist authored 3 years ago and Ammar Nejati committed 3 years ago

* C++17's `std::variant` is used instead of `boost::variant`.
* `std::stoi` and `std:stod` are used instead of `boost::lexical_cast`.
* `value_str` method is added to return a string representation of the option's value.

Layer editor improvements3

See merge request !420