Customise account balance for each account #2750

[sschiessl-bcp]

https://github.com/bitshares/bitshares-ui/issues/2750

• get familiar how currently the preferred asset is stored and balance calcluated, and what places in UI it impacts, report results in here
• essentially, all viewSettings are currently done on a global basis (meaning all viewsettings apply to all accounts on the computer), this request would require viewSettings/settings on a per-account basis. idea: add a new localStorage key that is similar to the existing one, but has "_accountname" as a postfix. when currentaccount is switched, those additional are used as well (overloading the currently existing viewsettings). the stores should not be different in their current usage
• the settings could then get a "for current account only" checkbox on the top

[VerevkinAlexander]

• The preferred asset is stored in the SettingsStore "unit" and calculated in the TotalBalanceValue. The "unit" is used in the AccountOrders, AccountOverwiev, AccountPortfolioList, AccountTreemap, AccountVoting, Fees, WithDrawModalNew, SettingsEntry, EquivalentPrice. In UI it impacts: AccountOverview, MarginPositiom, DashboardList & Header

[VerevkinAlexander]

@sschiessl-bcp should we do come thing with it or it can be closed?