Disable dynamic fee estimation by default

[smogm]

Set the default setting of the fee estimation to manual.

[HenryYoung42]

See related discussion project-ecc/eccoin#193

[HenryYoung42]

Having reviewed project-ecc/eccoin#193 again I am split on the correct solution. Fixing this in Electrum-ECC (as suggested by this issue's title) will require that all users upgrade to benefit from the fix. Fixing this in eccoind will mean we can update the two electrum servers and all users benefit from the fix with no client app release.