drag and drop fix for extmenu

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| Refs tickets  | #924
| License       | MIT
| Doc PR        |

see also https://gist.github.com/cmfcmf/6329308
Fixed Block filtering in 1.3.5/6

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| Refs tickets  | #516, #938
| License       | MIT
| Doc PR        |
Fixed displaying of selection boxes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #762
| Refs tickets  | #775
| License       | MIT
| Doc PR        |
added jpeg

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| Refs tickets  | #783
| License       | MIT
| Doc PR        |
Avoid flush by category selector

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| Refs tickets  | #1561
| License       | MIT
| Doc PR        |
some more fixes

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| Refs tickets  |
| License       | MIT
| Doc PR        |

do not know the tickets of this fixes