Add 1RM estimate (Brzycki's formula)

[realGWM]

Fixes #181

This patch adds 1RM (One Rep Max, see: https://en.wikipedia.org/wiki/One-repetition_maximum) estimation with Brzycki's formula to the charts.

Brzycki's (1) formula was chosen over Epley's (2) formula mainly because of ease of implementation ((2) does not work with 1rep).
(1) and (2) give exactly the same results for 10 reps, but for less than 10 reps (2) gives a slightly higher estimated maximum.
According to https://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1744&context=gs_rp (I've only read the conclusion at the end actually), (1) is more precise at 5 reps while (2) is more precise at 3 reps.

I decided to set the reps limit to 10 because it is believed that the formula becomes highly inaccurate for more than 10 reps, feel free to change this value if you want to.

[brodeurlv]

Thanks @realGWM, I will include this in the next release.

[realGWM]

I've just noticed that I forgot to remove unused import android.database.Cursor; from the PR, and Android Studio tells me that this is now the only unused import in the whole project 😞