(Feature) Add class="error to all to the errors <p> tags

[dennis00010011b]

Inspired by #767 (comment)

There is no way to find elements 'Error' on the page except use a xpath requests. But it is bad practice which leads to unstable e2e test.

Location where class="error still aren't added:

1. Step 2: Reserved tokens - Address
2. Step 2: Reserved tokens - Value
3. Step 3: Whitelist-Address
4. Step 3: Whitelist-Min
5. Step 3: Whitelist-Max
6. Step 3: Gasprice - Custom
7. Manage page: Start time
8. Manage page: End time
9. Manage page: Rate
10. Manage page: Supply
11. Manage page: Whitelist- Address
12. Manage page: Whitelist- Min
13. Manage page: Whitelist- Max

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