Check existence of selected block explorer using name string comparison
Check existence of selected block explorer using name string comparison

After further testing, I realized I introduced a bug in commit
4f4b0f6ce97878a81155aac29401b8206ed42c41 because apparently the
ArrayList.contains() method does not properly work for
BlockChainExplorer object - to fix this I implemented a new
contains() method that uses string comparison instead

bisq-network/exchange,bisq-network/exchange,bitsquare/bitsquare,bitsquare/bitsquare