adjust flag factor
remove costBase of Clue
remove costFactor of Clue
remove bonus_occupy from db schema
remove building_clue from db schema
remove factor of explore
remove factor of fire
integrate fire into clues
replace Clue with Skill
rename all clue related things
add table hero_skill
load skill when create hero
show skills menu according to offensive heroes' skill
show hero's skill in HeroLayer
disable skill if related offensive hero is dead
set dead offensive hero to gray
change offensive hero's Label to MenuItem
add the feature to reorder offensive heroes
update version info to v3.7