xreg for factors about mes

[config-i1]

Things to do:

1. initialiser: remove redundant values of B from xreg;
2. filler: get the ones that are there, reproduce the missing;
3. initialiser: share persistence values;
4. filler: get shared persistence values;
5. Deal with provided initials and factors;
6. xregSelector, update xregParametersMissing, xregParametersIncluded and xregParametersEstimated
7. provided xreg persistence
8. forecast.adam and xreg expansion

[config-i1]

(1) - (4) are done locally. Things to do:

1. Deal with provided initials and factors;
2. xregSelector, update xregParametersMissing, xregParametersIncluded and xregParametersEstimated
3. provided xreg persistence
4. forecast.adam and xreg expansion
5. FI=TRUE

[config-i1]

Only xregSelector left

[config-i1]

All done. But now refit() doesn't work with xreg

[config-i1]

Done