MSA: add distance matrix options

Discussed in https://ugene.unipro.ru/tracker/browse/UGENE-1362

The new options for the dialog could be:
o ignore 5' terminal gaps
o ignore 3' terminal gaps
o ignore internal gaps
o consecutive gaps as single difference (can't be selected if all previous "ignore" are marked)

Examples:
Consider a vs b from this multiple alignment (three sequences, so gaps present in both sequences are always ignored):
a -> -AAAUGE-NEE
b > --AEU-N-
c > EAAAUGEONE

*------------------
x ignore 5' terminal gaps
o ignore 3' terminal gaps
o ignore internal gaps
o consecutive gaps as single difference

a -> AAUGENEE
b > AEUN-
(3/8)

*------------------
o ignore 5' terminal gaps
x ignore 3' terminal gaps
o ignore internal gaps
o consecutive gaps as single difference

a -> AAAUGEN
b > -AEU-N
(3/7)

*------------------
o ignore 5' terminal gaps
o ignore 3' terminal gaps
x ignore internal gaps
o consecutive gaps as single difference

a -> AAAUNEE
b > -AEUN-
(3/7)

*------------------
o ignore 5' terminal gaps
o ignore 3' terminal gaps
o ignore internal gaps
x consecutive gaps as single difference

a -> AAAUGENEE
b > -AAUN-
(4/7) (7 instead of 9 columns)

Some combinations:

• • • • • • • • • • • • • • • • • • • equivalent to option "--iddef 0" in UCLUST
                                      x ignore 5' terminal gaps
                                      x ignore 3' terminal gaps
                                      x ignore internal gaps
                                      o consecutive gaps as single difference

a -> AAUN
b -> AEUN
(3/4)

• • • • • • • • • • • • • • • • • • • equivalent to option "--iddef 1" in UCLUST (I would leave this "simple identity" as default.
                                      o ignore 5' terminal gap
                                      o ignore 3' terminal gaps
                                      o ignore internal gaps
                                      o consecutive gaps as single difference

a -> AAAUGENEE
b > -AEUN-
(3/9)

• • • • • • • • • • • • • • • • • • • equivalent to option "--iddef 2" in UCLUST
                                      x ignore 5' terminal gap
                                      x ignore 3' terminal gaps
                                      o ignore internal gaps
                                      o consecutive gaps as single difference

a -> AAUGEN
b > AEU-N
(3/6)