HeliBoard 4.0-beta1

Changes since 4.0-alpha2:

• upgrade Bangla dictionary, by @RHJihan (#2574)
• add Toki Pona layout, by @dsremo (#2575)
• internal refactor for sanity, mostly by @devycarol (#2252)
• update list of punctuation symbols (#2493)
• add link to community part of readme in about section (#2566)
• avoid spellchecking some inapplicable "words" (#1102)
• make automatic input of shift-to-capitalize word optional (#2317)
• Korean combiner now ignores emojis (#1896)
• add setting for key hint font size (#2106)
• add colors for emoji search to "all colors" (#2442)
• workaround for Android 6 being unable to rotate some images by 90° (#943)
• distribute toolbar keys evenly over toolbar (there were some issues, may search later)
• keep all applicable dictionary information in background data gathering
• minor fixes and improvements