PN-257 Show gas estimate in confirmation window

[germanviescas]

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[sergevar]

• The light gray on white is hard to read, and it's the most important data. Need to highlight
• All hex fields should be with a 'mono' class, which should ensure the font is monospace (from, to, data raw...)
• Let's add some spaces in between data raw bytes. I think these can be achieved by spans of a small width instead of " ", so that: the space doesn't take the whole character width, and also when you copy-paste it it would be copied without spaces