Parsing of dnf.conf and repositories configuration must be locale independent

[jrohel]

Parsing of configuration files are now locale dependent - locale dependent function are used.

At least:

• std::stod is used for log_size, bandwidth, minrate, all options using class OptionSeconds
• std::stof for throttle

Now only the C locale is set. When the C++ locale is set, problems may occur, for example, when parsing using the >> operator.

Example of bad parsing:
The log_size = 1.6M option is not parsable in the Czech locale - Czech uses a comma (not a dot) as a decimal separator.
In log is WARNING Config error in section "main" key "log_size": Nelze převést '1.6M' na bajty