Fixed #408 - allow to set default account

...in/java/de/deadlocker8/budgetmaster/accounts/Account.java

.../deadlocker8/budgetmaster/accounts/AccountController.java

.../deadlocker8/budgetmaster/accounts/AccountRepository.java

.../de/deadlocker8/budgetmaster/accounts/AccountService.java

.../de/deadlocker8/budgetmaster/services/HelpersService.java

src/main/resources/languages/_de.properties

src/main/resources/languages/_en.properties

src/main/resources/static/js/main.js

src/main/resources/templates/accounts/accounts.ftl

src/main/resources/templates/accounts/newAccount.ftl

...resources/templates/transactions/newTransactionMacros.ftl