Improve granularity of automatic matrix- and tree-recalculation in ARB_DIST

[westram]

Matrix and are recalculated far to often / much.

Should not recalculate if

• non-sequence species data changes
• matrix changes, but matrix is disabled
• species marks change, but matrix was calculated for all

Should only recalculate affected column(s) of the matrix, if

• sequence data changes
• some species are marked/unmarked

Some of the above examples will be easier to implement with #420.

Should recalculate when

• number of bootstrap trees changes (-recalc only)
• when a second filter is activated (works)