fix: show balances and fees below 0.000001 as nonzero on the send screens (closes #343)

The stored ETH and token balances and the send-confirm screen's fee were each
cut to six decimal places, and a token holding cut to zero was dropped, so a
value below 0.000001 read as zero. Balances are now stored exactly, whatever
decimals a token declares, and every nonzero token holding is kept; the balance
check reads a token balance to its first 18 places. The balance lists, the
send-screen token selector, the address total and the remove-address warning
leave out a holding below 0.000001 themselves, through isBelowOneMillionth().
The send and send-confirm screens' balances, reserve and insufficient-balance
messages go through truncateAmountNeverZero(). The send-confirm and approval
screens both render the fee through formatFee(), which prices the exact fee in
USD.

Model: opus-5-5

src/popup/views/deleteAddress.js

@@ -87,7 +87,8 @@ function recoveryPathText(wallet) {
 // AddressDetail, followed by the USD total when there is one to give — no
 // total line at all on testnet or before the first price fetch, and no figure
 // when every holding here is one with no price, since "$0.00" directly under
-// "This address holds a balance." is a contradiction.
+// "This address holds a balance." is a contradiction. A token holding below
+// 0.000001 does not count, as the lines below leave it out.
 function balanceWarningHtml(addr) {
     if (!addressHoldsFunds(addr)) return " ";
     const line = formatAddressTotal(getAddressValue(addr));