RF: Widespread refactorings

With the aim of making the fsl/win-pytreatxrepository independent of any specific pytreat.

Pandas talk migrated to applications/pandas/.

fslpy practical migrated to applications/fsply/.

Python introduction talk migrated to getting_started/00_overview

added 2 commits

• 35a4d607 - RF: Fixes to readme and some paths
• 50f3826c - MNT: Re-render notebooks

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added 1 commit

• a2fbfa38 - MNT: Fix paths in fslpy practical

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merged

mentioned in commit 01bd0e12