[MODIFIED] delete the default sequence
[Delete] the default sequence = 0
[NEW]add new module res_currency_priority and change some things in mod second rate
[ADD] the method currency_priority

this method helps when the currency base is over the base currency
[MODIFIED] some changes in the mod current second rate and the priority
Merge pull request #130 from ClearCorp-dev/8.0-res_currency_sequence-rv

[MRG] Migration res currency sequence and currency_second_rate_BCCR