(Feature) use gasprice oracle on invest page

[igorbarinov]

Problem:
On invest page, we are using fixed price of 15 Gwei
Solution:
For Foundation network use the gasprice oracle with safe value

[vbaranov]

Reminder to assignee:
After merging #430 the gasprice oracle with safe value is used for each network.

[igorbarinov]

@vbaranov gasprice oracle is used only for mainnet.. we don't have oracles for other networks.

[vbaranov]

@igorbarinov yes, and this is why I added the reminder to this issue. Now ICO Wizard calculates slow price from oracle (where values are from mainnet) for every network. Is this correct, if, for example, for Core POA we have 1Gwei ?

[igorbarinov]

It is not correct. But not a problem.. Maybe it's good to show people how much transaction costs on the foundation network