Show log in dialog
Add vertical scrollbar for log
With dark theme but ugly text colors (no energy saving for LCD)
Fix bug: crash in deletion (usually last line of text)

This is due to getSpans being called (in superclass's replace method)
to regenerate text layout before the blocks are actually recomputed.
Currently, getSpans implementation assumes spans data (easily computed
from fields such as highlighted_blocks_positions, line_num_blocks_counts,
etc.) Due to old data, positions are not guaranteed to be in
correct range anymore! (This just somehow works!)