AccountActivity: make content underneath FABs accessible (bitfireAT/davx5#390)

* Doubled bottom padding

Signed-off-by: Arnau Mora <arnyminerz@proton.me>

* Account activity: increase margin for two FABs even more

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Signed-off-by: Arnau Mora <arnyminerz@proton.me>
Co-authored-by: Ricki Hirner <hirner@bitfire.at>