S3tbx 299 syn tie points

[TonioF]

This PR does not leave everything perfect, but it is an improvement.
Effects:

• Less memory usage
• Product opening takes less time
• Smoother image display by using Linear interpolation rather than Nearest Neighbour
• Tie point interpolation is restricted to regions where tie points are close

[TonioF]

While this PR poses a solution to the problem, we find that ultimately the problem is that the tie-point grids are not provided in an ideal way. We therefore decided to not read them at all instead and wait for an eventual change of the data format.
This PR will be kept open as long as we do not have an optimal solution.

[CLAassistant]

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